Method for heat recovery of a polyolefin plant and polyolefin heat recovery system

Abstract

The present application relates to the technical field of petroleum chemical industry, and discloses a heat recovery method and system for a polyolefin device, which uses the heat of the discharge of a high-density polyethylene device and / or a polypropylene device and / or a polyolefin elastomer device to heat the combustion air of a cracking furnace of an ethylene device, and has the advantage of reducing the energy consumption of the polyolefin device and the ethylene device.

Description

Technical Field

[0001] This invention relates to the field of petrochemical technology, and more specifically to a heat recovery method and a heat recovery system for a polyolefin plant. Background Technology

[0002] Sinopec Tianjin LNG Company and Sinopec Tianjin Nangang Ethylene Project are located in the same industrial zone. Through a mutually beneficial cooperation model of exchanging cold and heat resources, they have already exchanged the cold energy of the low-temperature LNG (-170℃) originally used by the natural gas branch for seawater and propylene vaporization with the surplus heat of the newly built 1.2 million tons / year ethylene plant. This coupled development approach achieves comprehensive regional development, reduces carbon emissions, and lowers the energy consumption per ton of product for the ethylene plant, thereby enhancing competitiveness through green advantages.

[0003] The 1.2 million tons / year ethylene unit of Sinopec's Tianjin Nangang ethylene project has several downstream polyolefin units (high-density polyethylene unit, polypropylene unit, and polyolefin elastomer unit). Each of these reaction systems generates a significant amount of low-temperature heat, which is not being utilized effectively in the existing units. Generally, circulating cooling water or chillers are used for cooling, which not only increases the consumption of water, electricity, and other energy sources but also results in the loss of a large amount of usable heat energy. Summary of the Invention

[0004] The purpose of this invention is to overcome the problem that existing technologies do not make reasonable use of ethylene and downstream supporting equipment, and that the use of circulating cooling water or chillers for cooling not only increases the consumption of energy such as water and electricity, but also loses a large amount of usable heat energy. This invention provides a heat recovery method and a polyolefin heat recovery system for polyolefin plants, which has the advantage of reducing the energy consumption of polyolefin plants and ethylene plants.

[0005] To achieve the above objectives, the present invention provides a heat recovery method for a polyolefin plant, the heat recovery method comprising: using the discharge heat from a high-density polyethylene plant and / or a polypropylene plant and / or a polyolefin elastomer plant to heat the combustion air of a cracking furnace in an ethylene plant.

[0006] A second aspect of the present invention provides a polyolefin heat recovery system, the polyolefin heat recovery system comprising an ethylene unit, a high-density polyethylene unit, a polypropylene unit, a polyolefin elastomer unit, and a heat exchange device, the heat exchange device being used to collect the heat from the discharge materials of the high-density polyethylene unit and / or the polypropylene unit and / or the polyolefin elastomer unit to heat the combustion air of the cracking furnace of the ethylene unit.

[0007] Through the above technical solution, the present invention uses the output heat of the high-density polyethylene unit and / or polypropylene unit and / or polyolefin elastomer unit to heat the combustion air of the cracking furnace of the ethylene unit. Compared with the existing technology where downstream ethylene supporting units cool down and remove heat through circulating cooling water or chillers, this reduces the consumption of energy such as water and electricity, while effectively utilizing thermal energy, and provides a process flow for energy optimization of the entire combined unit. Attached Figure Description

[0008] Figure 1 This is a schematic diagram of a polyolefin heat recovery system.

[0009] Explanation of reference numerals in the attached figures

[0010] 1. Ethylene unit; 2. High-density polyethylene unit; 3. Polypropylene unit; 4. Polyolefin elastomer unit; 5. Heat exchange medium replenishment pipeline. Detailed Implementation

[0011] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0012] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0013] This invention discloses a heat recovery method for a polyolefin plant, the heat recovery method comprising: using the output heat from a high-density polyethylene plant and / or a polypropylene plant and / or a polyolefin elastomer plant to heat the combustion air of a cracking furnace in an ethylene plant.

[0014] In existing technologies, the reaction heat of high-density polyethylene (HDPE), polypropylene (PP), and polyolefin elastomer (POE) plants is generally cooled and removed by circulating cooling water or a chiller. This not only increases the consumption of energy such as water and electricity but also results in the loss of a large amount of usable heat energy. This invention uses the heat from the output of HDPE and / or PP and / or POE plants to heat the combustion air of the cracking furnace in the ethylene plant. This reduces the energy consumption of the POE and ethylene plants while ensuring stable operation of the plants, thus achieving optimized energy utilization of the entire integrated plant.

[0015] Considering the total heat of reaction and temperature level of the HDPE and PP units, and to maximize heat recovery, the heat recovery method includes: S1 After the two heat exchange medium streams are used to collect the discharge heat of the HDPE and PP units respectively, they are combined into one heat exchange medium stream to collect the discharge heat of the polyolefin elastomer unit, and then exchanged with the feed of the ethylene unit.

[0016] The heat recovery method also includes: S2 dividing the heat exchange medium stream after heat exchange with the feed of the ethylene unit into two streams, and then performing S1. In this way, heat can be recycled and released between the ethylene unit and its downstream supporting high-density polyethylene unit, polypropylene unit, and polyolefin elastomer unit.

[0017] The heat collected by the heat exchange medium in S1 is used to preheat the air fed into the ethylene unit. It should be noted that in the prior art, the air preheater of the bottom burner of the cracking furnace in the ethylene unit requires a heat source for heating, such as using the 85°C quench water of the ethylene unit itself. This invention uses the heat collected from the high-density polyethylene unit, polypropylene unit, and polyolefin elastomer unit for the air preheater of the cracking furnace. While ensuring the stable operation of the unit, it reduces the energy consumption of the polyolefin unit and the ethylene unit. The saved 85°C quench water can be exchanged with other media in the ethylene unit for heat, further improving the utilization effect of the quench water.

[0018] The heat exchange medium stream includes at least one of demineralized water, chilled water, quench water, and cryogenic liquid.

[0019] In S1, the temperature of the heat transfer medium after heat exchange with the combustion air of the pyrolysis furnace of the ethylene unit is 40-60℃.

[0020] In S1, the temperature of the heat exchange medium stream formed by collecting the heat from the high-density polyethylene unit and the polypropylene unit and combining them is 40-70℃.

[0021] In S1, the temperature of the heat exchange medium stream after collecting the discharge heat from the polyolefin elastomer device is 75-85℃.

[0022] In S1, the total flow rate of the heat exchange medium is 500-600 t / h.

[0023] In S1, two heat exchange medium streams with a flow ratio of 4-2:3-1 are used to collect the discharge heat from the high-density polyethylene unit and the polypropylene unit, respectively.

[0024] In this invention, the annual output of the ethylene plant is 1.2 million tons / year of ethylene, the annual output of the high-density polyethylene plant is 500,000 tons / year of high-density polyethylene, the annual output of the polypropylene plant is 300,000 tons / year of polypropylene, and the annual output of the polyolefin elastomer plant is 100,000 tons / year of polyolefin elastomer. The heat of reaction for the 500,000 tons / year high-density polyethylene plant is 7.4 MW, the heat of reaction for the 300,000 tons / year polypropylene plant is 3.2 MW, and the heat of reaction for the 100,000 tons / year polyolefin elastomer plant is 13 MW, totaling 23.6 MW.

[0025] A second aspect of the present invention provides a polyolefin heat recovery system, which includes an ethylene unit 1, a high-density polyethylene unit 2, a polypropylene unit 3, a polyolefin elastomer unit 4, and a heat exchanger. The heat exchanger is used to collect the heat from the discharge material of the high-density polyethylene unit 2 and / or the polypropylene unit 3 and / or the polyolefin elastomer unit 4 to heat the combustion air of the cracking furnace of the ethylene unit.

[0026] The polyolefin heat recovery system of the present invention can recover heat through an intermediate medium for preheating the feed of ethylene unit 1, thereby realizing the process flow of energy optimization utilization of the entire combined unit.

[0027] The heat exchange device of the present invention includes:

[0028] The first heat exchanger has a cold material pipeline for circulating the combustion air of the cracking furnace of the ethylene unit, and a hot material pipeline for circulating the heat exchange medium.

[0029] The second heat exchanger has a hot material pipeline for the flow of the high-density polyethylene unit 2 discharge material and a cold material pipeline for the flow of the heat exchange medium.

[0030] The third heat exchanger has a hot material pipeline for the flow of the polypropylene unit 3 discharge and a cold material pipeline for the flow of the heat exchange medium.

[0031] The fourth heat exchanger has a hot material pipeline for the flow of the polyolefin elastomer unit 4, and the second heat exchanger has a cold material pipeline for the flow of the heat exchange medium.

[0032] The outlet ends of the cold material pipelines of the second and third heat exchangers are connected to the inlet end of the cold material pipeline of the fourth heat exchanger through a confluence pipe, and the outlet end of the cold material pipeline of the fourth heat exchanger is connected to the inlet end of the hot material pipeline of the first heat exchanger.

[0033] Furthermore, the hot material pipeline outlet of the first heat exchanger is connected to the cold material pipeline inlet of the second and third heat exchangers respectively through a split pipe, so as to realize the circulation of heat and heat release between the ethylene unit and the downstream supporting high-density polyethylene unit, polypropylene unit and polyolefin elastomer unit.

[0034] The first heat exchanger, the second heat exchanger, the third heat exchanger and the fourth heat exchanger are at least one of plate heat exchangers, fixed tube sheet heat exchangers and floating head heat exchangers.

[0035] The first heat exchanger is set as the air preheater of the bottom burner of the cracking furnace of the ethylene unit 1. The present invention introduces the heat collected from the high-density polyethylene unit, polypropylene unit and polyolefin elastomer unit into the existing air preheater of the cracking furnace, which can reduce the amount of modification work and reduce the energy consumption of the polyolefin unit and the ethylene unit while ensuring the stable operation of the unit.

[0036] The branch pipe and the merging pipe can be conventional Y-shaped pipe joints in the existing technology, and flow control valves can be installed on the branch pipes or main pipes of the branch pipe and the merging pipe according to actual needs.

[0037] Among them, the outlet end of the cold material pipeline of the fourth heat exchanger is connected to the inlet end of the hot material pipeline of the first heat exchanger, and a heat exchange medium replenishment pipeline 5 is connected to the pipeline. Thus, when the flow rate of the heat exchange medium, such as circulating demineralized water, is insufficient, appropriate replenishment is made.

[0038] The advantages of the present invention are illustrated by the following examples, but the present invention is not limited thereto.

[0039] Example

[0040] See also Figure 1 The polyolefin heat recovery system shown uses approximately 517 t / h of closed demineralized water as an intermediate medium (referred to as: heat medium water) to circulate and release heat in the 1.2 million tons / year ethylene unit and the downstream supporting 500,000 tons / year high-density polyethylene (HDPE) unit, 300,000 tons / year polypropylene (PP) unit, and 100,000 tons / year polyolefin elastomer (POE) unit.

[0041] Heating components:

[0042] (1) The hot water from the ethylene unit 1 at 45°C is divided into two streams and enters the HDPE unit and the PP unit. Among them, 316t / h of hot water enters the HDPE unit and 201t / h of hot water enters the PP unit. After passing through the plate heat exchanger, the two units obtain different reaction heats (10.7MW) and then merge them. After heat exchange, the temperature of the hot water reaches 64°C.

[0043] (2) The 64°C hot water enters the POE device and obtains the reaction heat (13MW) of the POE device through the plate heat exchanger. After heat exchange, the temperature of the hot water reaches 84°C.

[0044] Heat-generating part:

[0045] 84°C hot water enters the ethylene unit to provide a heat source (23MW) for the air preheater of the bottom burner of the ethylene unit's cracking furnace, heating the air and reducing the fuel consumption of the cracking furnace.

[0046] Compared to the downstream ethylene plants (high-density polyethylene plant, polypropylene plant, polyolefin elastomer plant) where the heat of reaction is cooled and removed by circulating cooling water, this method can recover 23MW of heat of reaction, reduce circulating water consumption by 4100t / h, and save approximately 23 million yuan in operating costs annually.

[0047] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various specific technical features in any suitable manner. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately. However, these simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for heat recovery in a polyolefin plant, characterized in that, The heat recovery method includes using the heat from the high-density polyethylene unit and / or polypropylene unit and / or polyolefin elastomer unit to heat the combustion air of the pyrolysis furnace of the ethylene unit.

2. The heat recovery method according to claim 1, wherein, The heat recovery method includes: S1 After the two heat exchange medium streams are used to collect the discharge heat of the high-density polyethylene unit and the polypropylene unit respectively, they are combined to form a heat exchange medium stream for collecting the discharge heat of the polyolefin elastomer unit, and then exchanged with the combustion air of the cracking furnace of the ethylene unit.

3. The heat recovery method according to claim 1 or 2, wherein, The heat recovery method includes: S2 dividing the heat exchange medium stream after heat exchange with the feed of the ethylene unit into two streams, and then performing S1.

4. The heat recovery method according to any one of claims 1-3, wherein, The temperature of the heat transfer fluid after the combustion air in the cracking furnace of the ethylene heating unit is 40-60℃.

5. The heat recovery method according to any one of claims 1-4, wherein, The heat exchange medium stream includes at least one of demineralized water, chilled water, quench water, and cryogenic liquid.

6. The heat recovery method according to any one of claims 1-5, wherein, In S1: The heat collected from the high-density polyethylene and polypropylene plants is combined to form a single heat exchange medium stream with a temperature of 40-70℃; and / or The temperature of the heat exchange medium stream after the discharge heat from the polyolefin elastomer collection device is 75-85℃.

7. The heat recovery method according to any one of claims 1-6, wherein, In S1: The total flow rate of the heat exchange medium is 500-600 t / h; and / or Two heat exchange medium streams with a flow ratio of 4-2:3-1 are used to collect the discharge heat from the high-density polyethylene unit and the polypropylene unit, respectively.

8. A polyolefin heat recovery system, characterized in that, The polyolefin heat recovery system includes an ethylene unit (1), a high-density polyethylene unit (2), a polypropylene unit (3), a polyolefin elastomer unit (4), and a heat exchanger. The heat exchanger is used to collect the heat from the discharge materials of the high-density polyethylene unit (2) and / or the polypropylene unit (3) and / or the polyolefin elastomer unit (4) to heat the combustion air of the cracking furnace of the ethylene unit (1).

9. The polyolefin heat recovery system according to claim 8, characterized in that, The heat exchange device includes: The first heat exchanger, the cold material line of the first heat exchanger is used to circulate the combustion air of the cracking furnace of the ethylene unit (1); The second heat exchanger, the hot material line of the second heat exchanger is used to circulate the discharge of the high-density polyethylene unit (2); The third heat exchanger, the hot material pipeline of the third heat exchanger is used to circulate the discharge of the polypropylene unit (3); The fourth heat exchanger, wherein the hot material pipeline of the fourth heat exchanger is used to circulate the discharge of the polyolefin elastomer device (4); The cold material pipelines of the second and third heat exchangers are used to circulate heat exchange medium and their outlet ends are connected to the inlet end of the cold material pipeline of the fourth heat exchanger through a confluence pipe. The outlet end of the cold material pipeline of the fourth heat exchanger is connected to the inlet end of the hot material pipeline of the first heat exchanger. Preferably, the hot material pipeline outlet of the first heat exchanger is connected to the cold material pipeline inlet of the second and third heat exchangers respectively via a branch pipe.

10. The polyolefin heat recovery system according to claim 9, characterized in that, The first, second, third, and fourth heat exchangers employ at least one of the following: plate heat exchangers, fixed tube sheet heat exchangers, and floating head heat exchangers; and / or The first heat exchanger is configured as an air preheater for the bottom burner of the pyrolysis furnace in the ethylene unit (1); and / or Each branch of the shunt pipe is equipped with a flow control valve; and / or A heat exchange medium replenishment pipeline (5) is connected to the pipeline that connects the outlet end of the cold material pipeline of the fourth heat exchanger to the inlet end of the hot material pipeline of the first heat exchanger.

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