Low-temperature waste heat recovery method of phenol-acetone device and system and application thereof

Abstract

The invention discloses a low-temperature waste heat recovery method and system of a phenol-acetone device and application of the low-temperature waste heat recovery method and system. The method comprises the following steps: generating first steam and first condensate by a low-pressure flash tank of a phenol-acetone device, and carrying out primary heat exchange on the first condensate and an oxidation feed to obtain the first condensate after heat exchange; changing the first condensate after heat exchange to normal pressure, mixing the first condensate with the second condensate to obtain third condensate, and performing secondary heat exchange on the third condensate and the gas-phase material at the top of the benzene tower to obtain third condensate after heat exchange; the third condensate obtained after heat exchange is subjected to pressure reduction and then subjected to flash evaporation treatment, low-temperature negative-pressure steam and condensate are generated, and part of the condensate serves as second condensate to be used; heating and pressurizing the low-temperature negative-pressure steam, and then carrying out steam-water separation to obtain second steam; the first steam and the second steam are optionally recycled. Waste heat of condensed water in the low-pressure flash tank is fully utilized, integrated heat exchange and optimized utilization are carried out on the waste heat and materials of the device, and the energy-saving and consumption-reducing effects are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of energy recovery of a phenol acetone device, and further to a low-temperature waste heat recovery method of a phenol acetone device, a system and an application thereof. Background Art

[0002] More than 90% of the phenol-acetone production processes in the prior art adopt the cumene method. That is, benzene and propylene react to obtain cumene; cumene is oxidized by oxygen or air to produce cumene hydroperoxide (CHP); CHP is decomposed to produce phenol and acetone. It can be seen that the cumene method of phenol-acetone production includes cumene oxidation, cumene hydroperoxide (CHP) concentration, CHP acid decomposition, sodium phenolate neutralization, phenol-acetone distillation, AMS hydrogenation and wastewater treatment.

[0003] The feed material of cumene oxidation in the existing phenol-acetone device needs to be preheated before going to the reactor, and the heating medium is the low-pressure steam produced by the low-pressure flash tank. In addition, the temperature of the gas phase medium at the top of the benzene tower in the existing phenol-acetone device is high, and the consumption of circulating cooling water by the top condenser is large. The steam condensate temperature of the low-pressure flash tank is high, and it is directly sent to the circulating water field outside the device for treatment, and the residual heat of the condensate is not recovered.

[0004] Therefore, the existing phenol acetone device has a high operating energy consumption. Based on energy-saving considerations, it is necessary to develop a low-temperature waste heat recovery method and a waste heat recovery system for the phenol acetone device. Summary of the invention

[0005] In order to solve the problems in the prior art, the present invention proposes a low-temperature waste heat recovery method for a phenol-acetone device, a system and an application thereof. The present invention fully utilizes the waste heat of low-pressure condensate water by setting a condensate water / oxidation feed heat exchanger, a condensate pump, a benzene tower top heat exchanger, a heat pump system and other equipment and a control process, and integrates heat exchange with the device materials for optimal utilization, thereby achieving energy saving and consumption reduction effects.

[0006] One of the objects of the present invention is to provide a low-temperature waste heat recovery method for a phenol acetone device, comprising the following steps:

[0007] (1) A low-pressure flash tank of a phenol-acetone device generates a first steam and a first condensate, and the first condensate is subjected to a heat exchange with an oxidation feed of the phenol-acetone device to obtain a first condensate after heat exchange;

[0008] (2) the first condensate after the heat exchange becomes atmospheric pressure and is mixed with the second condensate to obtain a third condensate, which is then subjected to secondary heat exchange with the gas phase material at the top of the benzene tower to obtain the third condensate after the heat exchange;

[0009] (3) The third condensate after the heat exchange is subjected to flash evaporation after being depressurized to produce low-temperature negative-pressure steam and condensate, and a portion of the condensate is used as the second condensate; the low-temperature negative-pressure steam is heated and pressurized, and then steam-water separation is performed to obtain the second steam; and the first steam and the second steam are optionally recycled.

[0010] In the technical solution of the present invention, the benzene tower refers to a common tower in which benzene substances are fed and participate in the reaction.

[0011] In the low-temperature waste heat recovery method of the phenol-acetone device of the present invention, preferably,

[0012] Step (1),

[0013] The condensate in the low-pressure flash tank is pressurized to a supercooled state and then heat exchanged again;

[0014] Preferably,

[0015] The first condensate is water; and / or,

[0016] The oxidation feed material comprises cumene; and / or,

[0017] Before the first heat exchange, the temperature of the first condensate is greater than the temperature of the oxidation feed.

[0018] In the low-temperature waste heat recovery method of the phenol-acetone device of the present invention, preferably,

[0019] Step (1),

[0020] Before the primary heat exchange, the temperature of the first condensate is 120-159° C., preferably 144-152° C.; for example, 120, 125, 130, 135, 140, 144, 145, 150, 152, 155, 159° C. and any parameter range between any two of the above values; and / or,

[0021] Before the primary heat exchange, the temperature of the oxidation feed is 20-45°C, preferably 30-40°C; for example, 20, 25, 30, 35, 40, 45°C and any parameter range between any two of the above values; and / or,

[0022] After the first heat exchange, the temperature of the oxidation feed is 75-90°C, preferably 80-85°C; for example, 75, 80, 85, 90°C and any parameter range between any two of the above values; and / or,

[0023] After one heat exchange, the first condensate temperature is 95-120° C., preferably 100-110° C.; for example, 95, 100, 110, 115, 120° C. and any parameter range between any two of the above values.

[0024] In the low-temperature waste heat recovery method of the phenol-acetone device of the present invention, preferably,

[0025] Step (2)

[0026] The first condensate after heat exchange is decompressed to normal pressure; and / or,

[0027] When the first condensate and the second condensate are mixed, the flow ratio of the first condensate to the second condensate is 0.75 to 0.9:1; preferably 0.8 to 0.85:1; for example, 0.75:1, 0.8:1, 0.85:1, 0.9:1 and any parameter range between any two of the above values; and / or,

[0028] The temperature of the second condensate is 76-90° C., preferably 83-88° C.; for example, 76, 80, 83, 85, 88, 90° C. and any parameter range between any two of the above values.

[0029] In the low-temperature waste heat recovery method of the phenol-acetone device of the present invention, preferably,

[0030] Step (2),

[0031] Before the secondary heat exchange, the temperature of the third condensate is lower than the temperature of the gas phase material at the top of the benzene tower;

[0032] Preferably,

[0033] The temperature of the gas phase material at the top of the benzene tower before heat exchange is 120-140°C, preferably 125-135°C; for example, 120, 125, 130, 135, 140°C and any parameter range between any two of the above values; and / or,

[0034] The temperature of the third condensate after heat exchange is 110-130° C., preferably 115-120° C.; for example, 110, 115, 120, 125, 130° C. and any parameter range between any two of the above values; and / or,

[0035] The gaseous material at the top of the benzene tower after the secondary heat exchange enters the condenser at the top of the benzene tower to undergo three heat exchanges with the circulating cooling water. After being completely condensed, it enters the gaseous condensate reflux tank at the top of the benzene tower.

[0036] In the low-temperature waste heat recovery method of the phenol-acetone device of the present invention, preferably,

[0037] Step (3),

[0038] The third condensate after heat exchange is decompressed to 40-70 kPaA, preferably 55-65 kPaA; for example, 40, 45, 50, 55, 60, 65, 70 kPaA and any parameter range between any two of the above values; and / or,

[0039] The vaporization rate of the flash treatment is in the range of 5%-10%; for example, 5%, 6%, 7%, 8%, 9%, 10% and any parameter range between any two of the above values; and / or,

[0040] The temperature range for increasing the temperature and pressure of the low-temperature negative pressure steam is 144-159°C, preferably 148-156°C; for example, 144, 148, 150, 153, 156, 159°C and any parameter range between any two of the above values; the pressure range is 0.3-0.5MPaG, preferably 0.35-0.45MPaG; for example, 0.3, 0.35, 0.4, 0.45, 0.5MPaG and any parameter range between any two of the above values

[0041] Preferably, a portion of the condensate after flash evaporation is used as the second condensate, and the rest is sent to the circulating water field as supplementary water.

[0042] In the low-temperature waste heat recovery method of the phenol-acetone device of the present invention, preferably,

[0043] Step (1),

[0044] During the start-up phase of the phenol-acetone unit, the oxidized feed is preheated by the first steam, and the preheated oxidized feed enters the benzene tower; when the unit runs stably, the preheating of the oxidized feed by the first steam is stopped, and the first condensate and the oxidized feed are subjected to a heat exchange treatment; the oxidized feed after the heat exchange treatment enters the benzene tower; and / or,

[0045] In the present invention, during the start-up stage of the phenol-acetone device, the low-pressure flash tank does not have time to produce condensate, and only low-pressure steam from the steam network can be used to heat the oxidative feed; when the device runs stably, the low-pressure flash tank produces condensate, and at this time, the valve for heating the oxidative feed with the first steam is cut off, and the first condensate is used instead of the first steam to heat the oxidative feed, so that the consumption of the first steam can be reduced;

[0046] During the start-up stage of the phenol acetone unit, the gaseous material at the top of the benzene tower is heat exchanged with the condenser at the top of the benzene tower, so that the gaseous material at the top of the benzene tower is completely condensed and then enters the gaseous condensate reflux tank at the top of the benzene tower; when the unit is running stably, the heat exchange between the gaseous material at the top of the benzene tower and the condenser at the top of the benzene tower is stopped, and the third condensate and the gaseous material at the top of the benzene tower are used for secondary heat exchange. After the secondary heat exchange, the gaseous material at the top of the benzene tower enters the condenser at the top of the benzene tower for a third heat exchange with the circulating cooling water, and enters the gaseous condensate reflux tank at the top of the benzene tower after being completely condensed.

[0047] In the present invention, during the feeding and starting stage, the gas phase at the top of the benzene tower does not have the first condensate and the second condensate, and circulating cooling water is used to perform heat exchange in the condenser at the top of the benzene tower, and the gas phase at the top of the tower enters the reflux tank after being completely condensed; when the device is running stably, the gas phase at the top of the benzene tower is firstly heat exchanged with the mixed condensate of the first condensate and the second condensate in the heat exchanger at the top of the benzene tower, and the gas phase is partially condensed, and then enters the condenser at the top of the benzene tower to perform heat exchange with the circulating cooling water, and enters the reflux tank after being completely condensed, thereby reducing the consumption of circulating cooling water.

[0048] The second object of the present invention is to provide a low-temperature waste heat recovery system for a phenol-acetone device, the waste heat recovery system comprising a low-pressure flash tank, a condensate pump, a condensate / oxidation feed heat exchanger, a normal-pressure condensate tank, a first delivery pump, a benzene tower top heat exchanger, a pressure reducing device and a heat pump system;

[0049] Among them, the first condensate outlet of the low-pressure flash tank is connected to the condensate pump, the hot side medium pipeline of the condensate / oxidation feed heat exchanger, the atmospheric condensate tank, the first delivery pump, the cold side medium pipeline of the benzene tower top heat exchanger, the pressure reducing device and the heat pump system in sequence; the cold side medium pipeline of the condensate / oxidation feed heat exchanger is provided with a feed port for the oxidation feed; the hot side medium pipeline of the benzene tower top heat exchanger is provided with a feed port for the gas phase material at the top of the benzene tower;

[0050] The second condensate outlet of the heat pump system is also connected to the cold side medium pipeline feed port of the benzene tower top heat exchanger; optionally, the first steam outlet of the low-pressure flash tank and the second steam outlet of the heat pump system are connected to the external steam network;

[0051] The low-temperature waste heat recovery method described in any one of the objectives of the present invention preferably adopts the system.

[0052] In the low-temperature waste heat recovery system of the present invention, preferably,

[0053] The heat pump system comprises a heat pump flash tank, a heat pump compressor, a heat pump gas-liquid separator tank and a second delivery pump; wherein the gas phase material outlet of the heat pump flash tank is connected to the gas phase feed port of the heat pump compressor and the heat pump gas-liquid separator tank in sequence; the condensate discharge port of the heat pump flash tank is connected to the second delivery pump, the second delivery pump is used to transport the second condensate, and the second condensate discharge port of the second delivery pump is connected to the cold side medium pipeline feed port of the benzene tower top heat exchanger; the liquid phase discharge port of the heat pump gas-liquid separator tank is connected to the circulating liquid feed port of the heat pump flash tank, and the steam discharge port of the heat pump gas-liquid separator tank is the second steam outlet of the heat pump system and is connected to the external steam pipe network;

[0054] Preferably, the heat pump system further comprises a steam reflux pipeline, and the feed inlet of the heat pump compressor is also connected to the steam discharge port of the heat pump gas-liquid separation tank.

[0055] In the low-temperature waste heat recovery system of the present invention, preferably,

[0056] A flow control device is provided on the pipeline for transporting the second condensate; and / or,

[0057] The heat pump gas-liquid separation tank is provided with a first liquid level control device; and / or,

[0058] The steam return pipeline is provided with a pressure control device; and / or,

[0059] The heat pump flash tank is provided with a second liquid level control device.

[0060] In the low-temperature waste heat recovery system of the present invention, preferably,

[0061] The condensate pump is selected from a delivery pump with a pressurizing function; and / or,

[0062] The pressure reducing device is selected from a pressure control device; preferably a pressure reducing valve; and / or,

[0063] The gas phase outlet of the heat pump flash tank is provided with a demister; and / or,

[0064] The heat pump compressor is a screw compressor.

[0065] In the low-temperature waste heat recovery system of the present invention, preferably,

[0066] The low-temperature waste heat recovery system also includes an oxidation feed preheater, the oxidation feed directly enters the cold side medium feed port of the oxidation feed preheater or the oxidation feed directly enters the cold side medium feed port of the condensate / oxidation feed heat exchanger, the cold side medium discharge port of the condensate / oxidation feed heat exchanger is connected to the cold side medium feed port of the oxidation feed preheater, the cold side medium discharge port of the oxidation feed preheater is connected to the feed port of the oxidation feed of the benzene tower; the hot side medium feed port of the oxidation feed preheater is connected to the first steam discharge port of the low-pressure flash tank; the hot side medium discharge port of the oxidation feed preheater is connected to the liquid feed port of the atmospheric pressure condensate tank; and / or,

[0067] The low-temperature waste heat recovery system also includes a benzene tower top condenser and a benzene tower top gas-phase condensate reflux tank; the hot side medium pipeline discharge port of the benzene tower top heat exchanger is connected with the hot side medium pipeline of the benzene tower top condenser and the benzene tower top gas-phase condensate reflux tank in sequence, and the benzene tower top gas-phase condensate reflux tank discharge port is connected with the benzene tower reflux liquid feed port, so that the material of the benzene tower top gas-phase condensate reflux tank can be refluxed to the benzene tower; preferably, the benzene tower top gas-phase material discharge port is also connected with the hot side medium feed port of the benzene tower top condenser; in this way, the benzene tower top gas-phase material can directly enter the benzene tower top condenser for heat exchange treatment.

[0068] The third object of the present invention is to provide a low-temperature waste heat recovery method as described in any one of the objects of the present invention or the low-temperature waste heat recovery system as described in any one of the second objects of the present invention for use in waste heat recovery in phenol acetone production, preferably in waste heat recovery in isopropylbenzene process phenol acetone production.

[0069] In the prior art, the oxidation feed needs to be heat exchanged to about 80-90°C by the oxidation feed preheater and the low-pressure steam produced by the low-pressure flash tank before entering the reactor. The condensate temperature of the low-pressure flash tank of the phenol acetone device is relatively high and is directly sent out of the device, and the low-temperature waste heat of the condensate is not recovered.

[0070] The present invention newly adds a condensate pump and a condensate / oxidation feed preheater. The condensate in the low-pressure flash tank can completely replace the low-pressure steam to exchange heat with the oxidation feed. The condensate is pressurized to a supercooled state by the condensate pump to avoid water hammer.

[0071] The steam condensate after heat exchange with the oxidation feed (i.e., the first condensate after heat exchange) enters the atmospheric pressure condensate tank. A benzene tower top heat exchanger is added to the top of the benzene tower. The condensate from the atmospheric pressure condensate tank is mixed with the steam condensate (i.e., the second condensate) produced by the newly added heat pump system and then heat exchanged with the gas phase at the top of the benzene tower, the heat of the gas phase at the top of the tower is recovered, and the gas phase at the top of the tower is condensed. The third condensate that has been heated up after heat recovery is decompressed and sent to the heat pump system. In the heat pump system, low-pressure steam is generated by the heat pump flash tank, which is sent to the heat pump compressor and compressed to high temperature and high pressure. After separation by the heat pump steam-water separator, the separated low-pressure steam (i.e., the second steam) is combined with the steam produced by the low-pressure flash tank (i.e., the first steam) into the low-pressure steam pipeline network to realize the recycling of steam. A part of the steam condensate separated by the heat pump system is used to supplement the atmospheric pressure condensate (i.e., the second condensate) of the heat exchanger at the top of the benzene tower, and the rest is sent out for treatment. The improved process of the present invention utilizes the low-temperature waste heat of low-pressure steam condensate to replace low-pressure steam and circulating cooling water for heat exchange with materials, and utilizes a heat pump to produce low-pressure steam.

[0072] The FC control loop (flow control loop) provided in the present invention is intended to perform constant flow control on the amount of the second condensate added, and to change the flow ratio of the first condensate to the second condensate by means of a flow setting value.

[0073] The PC control loop (pressure control loop) provided in the present invention is intended to control the condensate pressure after heat exchange to prevent the condensate from flashing before the pressure reducing valve. The pressure reducing valve is arranged close to the heat pump system to shorten the two-phase flow pipeline as much as possible.

[0074] In the technical solution of the present invention, the flow control device, liquid level control device, pressure control device, delivery pump with pressurizing function, and heat pump compressor used can be selected from existing commonly used devices as long as they can achieve the above functions.

[0075] The endpoints and any values ​​of the scope disclosed in the present invention are not limited to the precise scope or value, and these scopes or values ​​should be understood to include values ​​close to these scopes or values. For numerical ranges, the endpoint values ​​of each scope, the endpoint values ​​of each scope and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in this article. Hereinafter, in principle, each technical solution can be combined with each other to obtain a new technical solution, which should also be regarded as specifically disclosed in this article.

[0076] Compared with the prior art, the present invention has at least the following advantages:

[0077] The present invention achieves energy saving and consumption reduction by arranging equipment such as a condensate / oxidation feed heat exchanger, a condensate pump, a benzene tower top heat exchanger, a heat pump system, and a control process, making full use of the waste heat of low-pressure condensate, and optimizing the utilization of integrated heat exchange with the device materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0078] Figure 1 It is a schematic diagram of a material recovery system in a phenol-acetone device in the prior art;

[0079] Figure 2 It is a schematic diagram of a low-temperature waste heat recovery system of a phenol-acetone device of the present invention;

[0080] Figure 3 Schematic diagram of the heat pump system of the present invention.

[0081] Description of reference numerals:

[0082] 1-low-pressure flash tank, 2-condensate pump, 3-condensate / oxidation feed heat exchanger, 14-oxidation feed pipeline, 4-normal-pressure condensate tank, 5-first delivery pump, 6-benzene tower, 7-benzene tower top heat exchanger, 8-pressure reducing device, 9-heat pump system, 10-flow control device, 11-oxidation feed preheater, 12-benzene tower top condenser, 13-benzene tower top gas phase condensate reflux tank, 9-1-heat pump flash tank, 9-2-heat pump compressor, 9-3-heat pump gas-liquid separation tank, 9-4-second delivery pump, 9-5-first liquid level control device, 9-6-pressure control device, 9-7-second liquid level control device, 906-steam reflux pipeline. DETAILED DESCRIPTION

[0083] The present invention is described in detail below in conjunction with specific drawings and embodiments. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made to the present invention by those skilled in the art based on the content of the present invention still fall within the scope of protection of the present invention.

[0084] It should also be noted that the various specific technical features described in the following specific embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0085] In addition, the various embodiments of the present invention may be arbitrarily combined as long as they do not violate the concept of the present invention. The technical solutions thus formed belong to part of the original disclosure of this specification and also fall within the protection scope of the present invention.

[0086] The raw materials used in the examples and comparative examples, unless otherwise specified, are disclosed in the prior art, for example, they can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0087] Example 1

[0088] The low-temperature waste heat recovery system of the phenol-acetone device of the present invention mainly comprises Figure 2 The device shown in the dotted box includes a low-pressure flash tank 1, a condensate pump 2, a condensate / oxidation feed heat exchanger 3, a normal-pressure condensate tank 4, a first delivery pump 5, a benzene tower top heat exchanger 7, a pressure reducing device 8 and a heat pump system 9;

[0089] Among them, the first condensate outlet of the low-pressure flash tank is connected to the condensate pump, the hot side medium pipeline of the condensate / oxidation feed heat exchanger, the atmospheric condensate tank, the first delivery pump, the cold side medium pipeline of the benzene tower top heat exchanger, the pressure reducing device and the heat pump system in sequence; the cold side medium pipeline of the condensate / oxidation feed heat exchanger is provided with a feed port for oxidation feed, which is connected to the oxidation feed pipeline 14; the hot side medium pipeline of the benzene tower top heat exchanger is provided with a feed port for the benzene tower top gas phase material, and the benzene tower top gas phase material comes from the top of the benzene tower 6;

[0090] The heat pump system Figure 3 As shown, it includes a heat pump flash tank 9-1, a heat pump compressor 9-2, a heat pump gas-liquid separation tank 9-3 and a second delivery pump 9-4; wherein the gas phase material outlet of the heat pump flash tank is connected to the gas phase feed port of the heat pump compressor and the heat pump gas-liquid separation tank in sequence; the condensate discharge port of the heat pump flash tank is connected to the second delivery pump, the second delivery pump is used to transport the second condensate, and the second condensate discharge port of the second delivery pump is connected to the cold side medium pipeline feed port of the benzene tower top heat exchanger; the liquid phase discharge port of the heat pump gas-liquid separation tank is connected to the circulating liquid feed port of the heat pump flash tank, and the steam discharge port of the heat pump gas-liquid separation tank is the second steam outlet of the heat pump system connected to the external steam pipeline network;

[0091] The heat pump system also includes a steam reflux pipeline, and the feed inlet of the heat pump compressor is also connected to the steam discharge port of the heat pump gas-liquid separation tank;

[0092] The first steam outlet of the low-pressure flash tank 1 and the second steam outlet of the heat pump gas-liquid separation tank 9-3 are connected to the external steam network;

[0093] In the low-temperature waste heat recovery system of the present invention, a flow control device 10 is provided on the pipeline for transporting the second condensate; a first liquid level control device 9-5 is provided on the heat pump gas-liquid separation tank; a pressure control device 9-6 is provided on the steam reflux pipeline 906; and a second liquid level control device 9-7 is provided on the heat pump flash tank.

[0094] In the low-temperature waste heat recovery system of the present invention, the condensate pump is selected from a delivery pump with a pressurizing function; the pressure reducing device is selected from an existing commonly used pressure control device, which is a pressure reducing valve in this embodiment; the gas phase outlet of the heat pump flash tank is provided with a demister; and the heat pump compressor is a screw compressor.

[0095] The working process of the low temperature waste heat recovery system of the phenol acetone device of the present invention is as follows:

[0096] (1) exchanging heat once between the condensate in the low-pressure flash tank of the phenol-acetone device (the low-pressure flash tank is a device in the utility unit of the phenol-acetone device that collects condensate from medium- and high-pressure steam and flashes low-pressure steam, and the gas phase outlet is connected to the low-pressure steam network) and the oxidation feed of the phenol-acetone device to obtain a first condensate;

[0097] (2) After the first condensate becomes atmospheric pressure, it is mixed with the second condensate (the second condensate separated by the heat pump system is used as a supplement to the first condensate. After mixing with the first condensate, since the temperature of the second condensate is lower than that of the first condensate, the temperature of the first condensate can be reduced, which is beneficial to heat exchange with the gas phase at the top of the benzene tower to recover heat, and then a second heat exchange is performed with the gas phase material at the top of the benzene tower to obtain a third condensate after heat exchange;

[0098] (3) The third condensate is flash evaporated after being decompressed (enough gas phase will be flash evaporated only after the pressure is reduced to a certain level) to generate low-temperature negative-pressure steam and condensate, and a portion of the condensate is used as the second condensate; the low-temperature negative-pressure steam is heated and pressurized, and then steam-water separation is performed to obtain the second steam; the first steam and the second steam generated in the low-pressure flash tank are recovered and recycled.

[0099] The working process of heat pump system:

[0100] The third condensate is decompressed to negative pressure by the pressure reducing valve and enters the heat pump system. The third condensate flashes and separates low-temperature negative-pressure steam in the heat pump flash tank. It is sent to the heat pump compressor and compressed to high temperature and high pressure. After separation in the heat pump gas-liquid separation tank, the separated steam is merged into the low-pressure steam network to achieve steam recycling. The liquid phase of the heat pump gas-liquid separation tank is discharged into the heat pump flash tank. The low-temperature steam condensate discharged from the heat pump flash tank is sent out through the second delivery pump. Part of it is the second condensate, and the rest of the condensate goes to the circulating water field as supplementary water.

[0101] Example 2

[0102] like Figure 2 As shown, it is a schematic diagram of a low-temperature waste heat recovery system of a phenol acetone device of the present invention, and the low-temperature waste heat recovery system of a phenol acetone device of the present invention comprises a low-pressure flash tank 1, a condensate pump 2, a condensate / oxidation feed heat exchanger 3, a normal pressure condensate tank 4, a first delivery pump 5, a benzene tower top heat exchanger 7, a pressure reducing device 8 and a heat pump system 9;

[0103] Among them, the first condensate outlet of the low-pressure flash tank is connected to the condensate pump, the hot side medium pipeline of the condensate / oxidation feed heat exchanger, the atmospheric condensate tank, the first delivery pump, the cold side medium pipeline of the benzene tower top heat exchanger, the pressure reducing device and the heat pump system in sequence; the cold side medium pipeline of the condensate / oxidation feed heat exchanger is provided with a feed port for oxidation feed, which is connected to the oxidation feed pipeline 14; the hot side medium pipeline of the benzene tower top heat exchanger is provided with a feed port for the benzene tower top gas phase material, and the benzene tower top gas phase material comes from the top of the benzene tower 6;

[0104] The heat pump system Figure 3 As shown, it includes a heat pump flash tank 9-1, a heat pump compressor 9-2, a heat pump gas-liquid separation tank 9-3 and a second delivery pump 9-4; wherein the gas phase material outlet of the heat pump flash tank is connected to the gas phase feed port of the heat pump compressor and the heat pump gas-liquid separation tank in sequence; the condensate discharge port of the heat pump flash tank is connected to the second delivery pump, the second delivery pump is used to transport the second condensate, and the second condensate discharge port of the second delivery pump is connected to the cold side medium pipeline feed port of the benzene tower top heat exchanger; the liquid phase discharge port of the heat pump gas-liquid separation tank is connected to the circulating liquid feed port of the heat pump flash tank, and the steam discharge port of the heat pump gas-liquid separation tank is the second steam outlet of the heat pump system connected to the external steam pipeline network;

[0105] The heat pump system also includes a steam reflux pipeline, and the feed inlet of the heat pump compressor is also connected to the steam discharge port of the heat pump gas-liquid separation tank;

[0106] The first steam outlet of the low-pressure flash tank 1 and the second steam outlet of the heat pump gas-liquid separation tank 9-3 are connected to the external steam network;

[0107] In the low-temperature waste heat recovery system of the present invention, a flow control device 10 is provided on the pipeline for transporting the second condensate; a first liquid level control device 9-5 is provided on the heat pump gas-liquid separation tank; a pressure control device 9-6 is provided on the steam reflux pipeline 906; and a second liquid level control device 9-7 is provided on the heat pump flash tank.

[0108] In the low-temperature waste heat recovery system of the present invention, the condensate pump is selected from a delivery pump with a pressurizing function; the pressure reducing device is selected from an existing commonly used pressure control device, which is a pressure reducing valve in this embodiment; the gas phase outlet of the heat pump flash tank is provided with a demister; and the heat pump compressor is a screw compressor.

[0109] In the low-temperature waste heat recovery system of the present invention, the low-temperature waste heat recovery system also includes an oxidation feed preheater 11, the oxidation feed directly enters the cold side medium feed port of the oxidation feed preheater or the cold side medium feed port of the oxidation feed preheater 11 is connected to the cold side medium discharge port of the condensate / oxidation feed heat exchanger 3; the hot side medium feed port of the oxidation feed preheater 11 is connected to the first steam discharge port of the low-pressure flash tank 1; the cold side medium discharge port of the oxidation feed preheater 1 is connected to the feed port of the oxidation feed of the benzene tower 6; the hot side medium discharge port of the oxidation feed preheater 11 is connected to the liquid feed port of the atmospheric pressure condensate tank 4;

[0110] The low-temperature waste heat recovery system also includes a benzene tower top condenser 12 and a benzene tower top gas-phase condensate reflux tank 13; the hot side medium pipeline discharge port of the benzene tower top heat exchanger 7 is connected with the hot side medium pipeline of the benzene tower top condenser 12 and the benzene tower top gas-phase condensate reflux tank 13 in sequence, and the discharge port of the benzene tower top gas-phase condensate reflux tank 13 is connected with the reflux liquid feed port of the benzene tower 6, so that the material of the benzene tower top gas-phase condensate reflux tank can be refluxed to the benzene tower, and another part of the material of the benzene tower top gas-phase condensate reflux tank 13 can be extracted from the system; the benzene tower top gas-phase material discharge port is also connected with the hot side medium feed port of the benzene tower top condenser; it enters the benzene tower top condenser for heat exchange treatment; in this way, the benzene tower top gas-phase material can directly enter the benzene tower top condenser for heat exchange treatment.

[0111] Comparative Example 1

[0112] like Figure 1 As shown, it is a schematic diagram of the material recovery system in the phenol acetone device in the prior art; wherein, it includes a low-pressure flash tank 1, an oxidation feed preheater 11 and an atmospheric condensate tank 4; wherein, the first steam outlet of the low-pressure flash tank is connected to the hot side medium feed port of the oxidation feed preheater 11; the oxidation feed pipeline 14 is connected to the cold side medium feed port of the oxidation feed preheater 11; the hot side medium outlet of the oxidation feed preheater 11 is connected to the liquid feed port of the atmospheric condensate tank 4; the liquid in the atmospheric condensate tank 4 is transported to the circulating water field by a pump; the cold side medium outlet of the oxidation feed preheater 1 is connected to the feed port of the oxidation feed of the benzene tower 6; it can be seen that in the prior art, the oxidation feed needs to be heat exchanged with the low-pressure steam produced by the oxidation feed preheater before entering the reactor, while the condensate temperature of the low-pressure flash tank of the phenol acetone device is relatively high, but it is not used to directly send out the device, and the low-temperature waste heat of the condensate of the low-pressure flash tank is not recovered.

[0113] The phenol-acetone device in the prior art also includes a benzene tower top condenser 12 and a benzene tower top gas-phase condensate reflux tank 13; the benzene tower top gas-phase material discharge port is connected to the benzene tower top condenser hot side medium feed port; enter the benzene tower top condenser for heat exchange treatment, the benzene tower top condenser hot side material discharge port is connected to the benzene tower top gas-phase condensate reflux tank feed port; the benzene tower top gas-phase condensate reflux tank discharge refluxes to the benzene tower. It can be seen that the benzene tower top gas-phase medium temperature in the phenol-acetone device in the prior art is high, and the circulating cooling water consumption of only the tower top condenser is large, and the energy consumption is high.

[0114] Example 3

[0115] The low-temperature waste heat recovery method of the phenol-acetone device is carried out using the system shown in Example 2, and comprises the following steps:

[0116] (1) A low-pressure flash tank of a phenol-acetone device generates a first steam and a first condensate, and the first condensate is subjected to a heat exchange with an oxidation feed of the phenol-acetone device to obtain a first condensate after heat exchange; wherein the condensate in the low-pressure flash tank is pressurized to a supercooled state and then subjected to a heat exchange; the first condensate is water; the material of the oxidation feed is cumene; before the first heat exchange, the temperature of the first condensate is greater than the temperature of the oxidation feed;

[0117] Before the first heat exchange, the temperature of the first condensate is 148°C; before the first heat exchange, the temperature of the oxidation feed is 40°C.

[0118] After one heat exchange, the temperature of the oxidation feed is 85°C, and after one heat exchange, the temperature of the first condensate is 100°C.

[0119] (2) The first condensate after the heat exchange becomes atmospheric pressure and is mixed with the second condensate to obtain a third condensate, which is then subjected to secondary heat exchange with the gas phase material at the top of the benzene tower to obtain the third condensate after the heat exchange; wherein, when the first condensate and the second condensate are mixed, the flow ratio of the first condensate to the second condensate is 0.85:1; and the temperature of the second condensate is 86° C.;

[0120] Before the secondary heat exchange, the temperature of the third condensate is lower than the temperature of the gas phase material at the top of the benzene tower; the temperature of the gas phase material at the top of the benzene tower before the heat exchange is 131°C; the temperature of the third condensate after the heat exchange is 118°C; the gas phase material at the top of the benzene tower after the secondary heat exchange enters the top condenser of the benzene tower and undergoes three heat exchanges with the circulating cooling water, and enters the gas phase condensate reflux tank at the top of the benzene tower after all condensation;

[0121] (3) The third condensate after the heat exchange is depressurized and then flash-evaporated to produce low-temperature negative-pressure steam and condensate, and a portion of the condensate is used as the second condensate; the low-temperature negative-pressure steam is heated and pressurized, and then steam-water separation is performed to obtain second steam, and the first steam and the second steam are recycled; wherein, the third condensate after the heat exchange is depressurized to 67 kPaA; the vaporization rate of the flash evaporation is 6%; the temperature of heating and pressurizing the low-temperature negative-pressure steam is 148°C and the pressure is 0.35 MPaG; a portion of the condensate after the flash evaporation is used as the second condensate, and the rest is sent to the circulating water field as make-up water.

[0122] In addition, during the start-up phase of the phenol-acetone unit, the oxidized feed is preheated by the first steam, and the preheated oxidized feed enters the benzene tower; when the unit is running stably, the first steam is stopped to preheat the oxidized feed, and the first condensate and the oxidized feed are subjected to a heat exchange treatment; the oxidized feed after the heat exchange treatment enters the benzene tower;

[0123] During the start-up stage of feeding and loading of phenol acetone unit: the gaseous material at the top of benzene tower is heat exchanged with the condenser at the top of benzene tower, so that the gaseous material at the top of benzene tower is completely condensed and then enters the gaseous condensate reflux tank at the top of benzene tower; when the operation of the unit is stable, the heat exchange between the gaseous material at the top of benzene tower and the condenser at the top of benzene tower is stopped, and the third condensate and the gaseous material at the top of benzene tower are used for secondary heat exchange. After the secondary heat exchange, the gaseous material at the top of benzene tower enters the condenser at the top of benzene tower and undergoes tertiary heat exchange with the circulating cooling water, and then enters the gaseous condensate reflux tank at the top of benzene tower after being completely condensed.

[0124] Compared with the process of comparative example 1, the steam condensate after heat exchange with the oxidation feed (i.e., the first condensate after heat exchange) of the present invention enters the atmospheric condensate tank. A benzene tower top heat exchanger is added to the top of the benzene tower. The condensate from the atmospheric condensate tank is mixed with the steam condensate (i.e., the second condensate) output by the newly added heat pump system and then heat exchanged with the gas phase at the top of the benzene tower, the heat of the gas phase at the top of the tower is recovered, and the gas phase at the top of the tower is condensed. The third condensate that is heated after heat recovery is decompressed and sent to the heat pump system. In the heat pump system, low-pressure steam is generated by passing through the heat pump flash tank, which is sent to the heat pump compressor and compressed to high temperature and high pressure. After separation by the heat pump steam-water separator, the separated low-pressure steam (i.e., the second steam) is merged with the steam output from the low-pressure flash tank (i.e., the first steam) into the low-pressure steam pipeline network to realize the recycling of steam. A part of the steam condensate separated by the heat pump system is used to supplement the atmospheric condensate (i.e., the second condensate) of the heat exchanger at the top of the benzene tower, and the rest is sent out for treatment. The improved process of the present invention utilizes the low-temperature waste heat of low-pressure steam condensate (i.e., the first condensate produced by the low-pressure flash tank) to replace low-pressure steam and circulating cooling water for heat exchange with materials, and uses a heat pump to produce low-pressure steam.

[0125] Compared with the process of comparative example 1, the energy-saving effect of the process of embodiment 3 of the present invention is as follows: under the scale of 200,000 tons of phenol acetone device, it is expected to reduce 300t / h of circulating cooling water, and produce 6.4t / h of low-pressure steam, and reduce the comprehensive energy consumption by 5kg standard oil / t product.

[0126] Comparative Example 2

[0127] It adopts a process that is basically the same as that of Example 3, with the only difference being that the third condensate after heat exchange does not enter the heat pump system, and the third condensate after heat exchange is discharged from the system.

[0128] Compared with Example 3, Comparative Example 2 cannot produce the second steam and the second condensate, and its energy recovery result is poor and the comprehensive energy consumption is high; and because Comparative Example 2 does not produce a second condensate with a temperature lower than that of the first condensate, the heat exchange effect of the gas phase material at the top of the benzene tower in the top heat exchanger of the benzene tower is reduced, and accordingly, the amount of circulating cooling water used will also increase significantly.

[0129] The present invention has been described in detail above in conjunction with specific implementations and exemplary examples, but these descriptions cannot be understood as limiting the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, a variety of equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its implementation methods, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be subject to the attached claims.

[0130] All publications, patent applications, patents and other references mentioned in this specification are incorporated herein by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings conventionally understood by those skilled in the art. In the event of a conflict, the definition in this specification shall prevail.

[0131] When this specification uses the prefix "well-known to those skilled in the art", "prior art" or similar terms to introduce materials, substances, methods, steps, devices or components, etc., the objects introduced by the prefix cover those commonly used in the art when this application is filed, but also include those that are not commonly used at present but will become recognized in the art as being suitable for similar purposes.

[0132] In the context of the present specification, any matters or items not mentioned are directly applicable to those known in the art without any changes except those explicitly stated.

Claims

1. A method for recovering low-temperature waste heat from a phenol-acetone device, comprising the following steps: (1) A low-pressure flash tank of a phenol-acetone device generates a first steam and a first condensate, and the first condensate is subjected to a heat exchange with an oxidation feed of the phenol-acetone device to obtain a first condensate after heat exchange; (2) converting the first condensate after heat exchange to normal pressure and mixing it with the second condensate to obtain a third condensate, and then performing a secondary heat exchange with the gas phase material at the top of the benzene tower to obtain the third condensate after heat exchange; (3) The third condensate after the heat exchange is subjected to flash evaporation after being depressurized to produce low-temperature negative-pressure steam and condensate, and a portion of the condensate is used as the second condensate; the low-temperature negative-pressure steam is heated and pressurized, and then steam-water separation is performed to obtain the second steam; and the first steam and the second steam are optionally recycled.

2. The low-temperature waste heat recovery method of the phenol-acetone device according to claim 1, characterized in that: Step (1), The condensate in the low-pressure flash tank is pressurized to a supercooled state and then heat exchanged again; Preferably, The first condensate is water; and / or, The oxidation feed material comprises cumene; and / or, Before the first heat exchange, the temperature of the first condensate is greater than the temperature of the oxidation feed.

3. The low-temperature waste heat recovery method of the phenol-acetone device according to claim 1, characterized in that: Step (1), Before the first heat exchange, the temperature of the first condensate is 120-159° C., preferably 144-152° C.; and / or, Before the primary heat exchange, the temperature of the oxidation feed is 20 to 45°C, preferably 30 to 40°C; and / or, After the first heat exchange, the temperature of the oxidation feed is 75 to 90° C., preferably 80 to 85° C.; and / or, After one heat exchange, the first condensate temperature is 95-120°C, preferably 100-110°C.

4. The low-temperature waste heat recovery method of the phenol-acetone device according to claim 1, characterized in that: Step (2) The first condensate after heat exchange is decompressed to normal pressure; and / or, When the first condensate and the second condensate are mixed, the flow ratio of the first condensate to the second condensate is 0.75 to 0.9:1; preferably 0.8 to 0.85:1; and / or, The temperature of the second condensate is 76 to 90°C, preferably 83 to 88°C.

5. The low-temperature waste heat recovery method of the phenol-acetone device according to claim 1, characterized in that: Step (2), Before the secondary heat exchange, the temperature of the third condensate is lower than the temperature of the gas phase material at the top of the benzene tower; Preferably, The temperature of the gas phase material at the top of the benzene tower before heat exchange is 120-140° C., preferably 125-135° C.; and / or, The temperature of the third condensate after heat exchange is 110-130° C., preferably 115-120° C.; and / or, After the secondary heat exchange, the gaseous material at the top of the benzene tower enters the condenser at the top of the benzene tower and undergoes three heat exchanges with the circulating cooling water. After being completely condensed, it enters the gaseous condensate reflux tank at the top of the benzene tower.

6. The low-temperature waste heat recovery method of the phenol-acetone device according to claim 1, characterized in that: Step (3), The third condensate after heat exchange is depressurized to 40-70 kPaA, preferably 55-65 kPaA; and / or, The vaporization rate of the flash treatment is in the range of 5%-10%; and / or, The temperature range for increasing the temperature and pressure of the low-temperature negative pressure steam is 144-159° C., preferably 148-156° C., and the pressure range is 0.3-0.5 MPaG, preferably 0.35-0.45 MPaG; Preferably, a portion of the condensate after flash evaporation is used as the second condensate, and the rest is sent to the circulating water field as supplementary water.

7. The low-temperature waste heat recovery method of the phenol-acetone device according to claim 1, characterized in that: Step (1), During the start-up phase of the phenol-acetone unit, the oxidized feed is preheated by the first steam, and the preheated oxidized feed enters the benzene tower; when the unit runs stably, the preheating of the oxidized feed by the first steam is stopped, and the first condensate and the oxidized feed are subjected to a heat exchange treatment; the oxidized feed after the heat exchange treatment enters the benzene tower; and / or, During the start-up stage of the phenol acetone unit, the gaseous material at the top of the benzene tower is heat exchanged with the condenser at the top of the benzene tower, so that the gaseous material at the top of the benzene tower is completely condensed and then enters the gaseous condensate reflux tank at the top of the benzene tower; when the unit is running stably, the heat exchange between the gaseous material at the top of the benzene tower and the condenser at the top of the benzene tower is stopped, and the third condensate and the gaseous material at the top of the benzene tower are used for secondary heat exchange. After the secondary heat exchange, the gaseous material at the top of the benzene tower enters the condenser at the top of the benzene tower for a third heat exchange with the circulating cooling water, and enters the gaseous condensate reflux tank at the top of the benzene tower after being completely condensed.

8. A low temperature waste heat recovery system for a phenol acetone device, characterized in that: The waste heat recovery system includes a low-pressure flash tank, a condensate pump, a condensate / oxidation feed heat exchanger, a normal-pressure condensate tank, a first delivery pump, a benzene tower top heat exchanger, a pressure reducing device and a heat pump system; Among them, the first condensate outlet of the low-pressure flash tank is connected to the condensate pump, the hot side medium pipeline of the condensate / oxidation feed heat exchanger, the atmospheric condensate tank, the first delivery pump, the cold side medium pipeline of the benzene tower top heat exchanger, the pressure reducing device and the heat pump system in sequence; the cold side medium pipeline of the condensate / oxidation feed heat exchanger is provided with a feed port for the oxidation feed; the hot side medium pipeline of the benzene tower top heat exchanger is provided with a feed port for the gas phase material at the top of the benzene tower; The second condensate outlet of the heat pump system is also connected to the cold side medium pipeline feed port of the benzene tower top heat exchanger; optionally, the first steam outlet of the low-pressure flash tank and the second steam outlet of the heat pump system are connected to the external steam network; The low-temperature waste heat recovery method described in any one of claims 1 to 7 preferably adopts the system.

9. The low temperature waste heat recovery system according to claim 8, characterized in that: The heat pump system comprises a heat pump flash tank, a heat pump compressor, a heat pump gas-liquid separator tank and a second delivery pump; wherein the gas phase material outlet of the heat pump flash tank is connected to the gas phase feed port of the heat pump compressor and the heat pump gas-liquid separator tank in sequence; the condensate discharge port of the heat pump flash tank is connected to the second delivery pump, the second delivery pump is used to transport the second condensate, and the second condensate discharge port of the second delivery pump is connected to the cold side medium pipeline feed port of the benzene tower top heat exchanger; the liquid phase discharge port of the heat pump gas-liquid separator tank is connected to the circulating liquid feed port of the heat pump flash tank, and the steam discharge port of the heat pump gas-liquid separator tank is the second steam outlet of the heat pump system and is connected to the external steam pipeline network; Preferably, the heat pump system further comprises a steam reflux pipeline, and the feed inlet of the heat pump compressor is also connected to the steam discharge port of the heat pump gas-liquid separation tank.

10. The low temperature waste heat recovery system according to claim 9, characterized in that: A flow control device is provided on the pipeline for transporting the second condensate; and / or, The heat pump gas-liquid separation tank is provided with a first liquid level control device; and / or, The steam return pipeline is provided with a pressure control device; and / or, The heat pump flash tank is provided with a second liquid level control device.

11. The low temperature waste heat recovery system according to claim 9, characterized in that: The condensate pump is selected from a delivery pump with a pressurizing function; and / or, The pressure reducing device is selected from a pressure control device; preferably a pressure reducing valve; and / or, The gas phase outlet of the heat pump flash tank is provided with a demister; and / or, The heat pump compressor is a screw compressor.

12. The low temperature waste heat recovery system according to claim 9, characterized in that: The low-temperature waste heat recovery system also includes an oxidation feed preheater, the oxidation feed directly enters the cold side medium feed port of the oxidation feed preheater or the oxidation feed directly enters the cold side medium feed port of the condensate / oxidation feed heat exchanger, the cold side medium discharge port of the condensate / oxidation feed heat exchanger is connected to the cold side medium feed port of the oxidation feed preheater, the cold side medium discharge port of the oxidation feed preheater is connected to the feed port of the oxidation feed of the benzene tower; the hot side medium feed port of the oxidation feed preheater is connected to the first steam discharge port of the low-pressure flash tank; the hot side medium discharge port of the oxidation feed preheater is connected to the liquid feed port of the atmospheric pressure condensate tank; and / or, The low-temperature waste heat recovery system also includes a benzene tower top condenser and a benzene tower top gas phase condensate reflux tank; the hot side medium pipeline discharge port of the benzene tower top heat exchanger is sequentially connected to the hot side medium pipeline of the benzene tower top condenser and the benzene tower top gas phase condensate reflux tank, and the benzene tower top gas phase condensate reflux tank discharge port is connected to the benzene tower reflux liquid feed port; Preferably, the gas phase material discharge port at the top of the benzene tower is also connected to the hot side medium feed port of the condenser at the top of the benzene tower.

13. An application of the low-temperature waste heat recovery method according to any one of claims 1 to 7 or the low-temperature waste heat recovery system according to any one of claims 8 to 12 in waste heat recovery in phenol acetone production, preferably in waste heat recovery in phenol acetone production by the isopropylbenzene process.

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