Process flow of reaction water injection for hydrogenation device

Abstract

This invention discloses a process flow for water injection in a hydrogenation unit. It uses condensate from high-pressure (4.0–3.5 MPa) or medium-pressure steam (1.0–2.0 MPa) as the injection water, continuously injected before the amine salt crystallization temperature along with the reaction effluent or before the high-pressure gas heat exchanger, eliminating the need for a continuous water injection point before the air cooler. Compared with existing technologies, this method offers the following advantages: it minimizes the impact of water injection on the heat exchange of the high-pressure medium, maximizing heat recovery; it avoids the risk of intermittent water injection before conventional heat exchangers; it saves on water injection pipelines and valves before the high-pressure air cooler; and it incidentally recovers the heat from the high-temperature condensate, reducing overall plant energy consumption.

Description

Technical Field

[0001] This invention pertains to a process flow for water injection in a hydrogenation unit within the petrochemical field, specifically relating to a method for injecting water into the reaction effluent or hot high-density gas of a hydrogenation unit. Background Technology

[0002] With the increasing weight and quality of crude oil being processed, stricter environmental protection requirements, and a market demand for cleaner and lower-carbon petroleum products, petrochemical companies are facing intensified competition. Impurities such as sulfur, nitrogen, and chlorine in the feedstock are converted into hydrogen sulfide, hydrogen chloride, and ammonia during the hydrogenation reaction. Under certain conditions, ammonia and hydrogen chloride can form ammonium salt deposits in the high-pressure heat exchanger of the hydrogenation unit's effluent system. This leads to increased pressure drop in the effluent system, decreased heat exchanger efficiency, and increased energy consumption. Ammonium salt deposits can also cause blockages, affecting the circulating hydrogen flow and causing compressor surge. Furthermore, under certain conditions, ammonium salt crystallization can absorb moisture from the reaction products, leading to under-deposit corrosion, which seriously affects the long-term safe operation of the hydrogenation unit. This has become an increasingly important issue for many design firms and owners.

[0003] In hydrogenation units, since the reaction process is highly exothermic, the efficient utilization of heat from the reaction effluent or hot high-temperature gas can reduce the unit's operating energy consumption. Existing units typically use this high-temperature medium (reaction effluent or hot high-temperature gas) to heat the cold process medium within the unit to the required temperature before sending it to a high-pressure air cooler for cooling. Simultaneously, to recover heat as much as possible and reduce energy consumption, the inlet temperature of the high-pressure air cooler needs to be minimized. During the heat exchange and cooling process of the reaction effluent or hot high-temperature gas, due to the presence of hydrogen sulfide and ammonia, ammonium chloride and ammonium hydrosulfide crystallize as the medium temperature decreases. The crystallization temperature of ammonium chloride is generally between 176-204℃, and that of ammonium hydrosulfide is approximately 26-65℃. Once ammonium salt crystallization occurs, it can clog pipelines and cause corrosion.

[0004] Chinese patent CN101655336A discloses an optimization method for water injection in an air cooler system for hydrogenation reaction effluent. By reading relevant data from the DCS (Distributed Control System) and combining it with relevant raw material analysis data, the optimal water injection method, flow rate, and location are calculated. This method allows for adjustment of the water injection location based on the actual operating conditions of the unit. However, on the one hand, this method requires water injection points to be set up before all heat exchangers and the air cooler, resulting in a large initial investment; on the other hand, it cannot solve the impact of continuous water injection before the heat exchangers on the heat exchange process.

[0005] To avoid this situation and ensure long-term safe operation of the equipment, the process design typically includes high-pressure continuous water injection before air cooling to dissolve ammonium salts and prevent blockage and corrosion. Intermittent water injection is installed before one or more upstream heat exchangers to temporarily handle ammonium salt crystallization. However, intermittent water injection has two main drawbacks: firstly, the reaction water temperature is generally low, which can severely impact the heat recovery of the reaction effluent or hot high-temperature gas; secondly, determining whether to initiate intermittent water injection requires an increase in the heat exchanger pressure drop, at which point salt formation may already be severe, posing a significant risk. Summary of the Invention

[0006] The purpose of this invention is to provide a process flow for water injection in a hydrogenation unit, which can both satisfy the purpose of water injection to flush ammonium salts on the medium side, and minimize the impact on the heat exchange of the medium while maximizing the removal of heat from the high-pressure medium; at the same time, it can also reduce engineering investment; thereby achieving the goal of avoiding the impact of intermittent operation on production stability, minimizing the risks caused by intermittent operation, and reducing the energy consumption of the unit operation.

[0007] Hydrogenation units typically inject water before the high-pressure air cooler to dissolve the released ammonium salts and prevent blockage of the air cooler's heat exchange tubes. Deoxygenated water is generally used for this pre-cooling water injection.

[0008] To achieve the above objectives, the technical solution adopted by the present invention to solve its technical problem is as follows:

[0009] A process flow for water injection in a hydrogenation unit is characterized in that: condensate from high-pressure steam or medium-pressure steam is used as reaction injection water in the hydrogenation unit, and is continuously injected before the heat exchanger before the crystallization temperature of the reaction effluent or hot high-temperature amine salt.

[0010] The pressure of the high-pressure steam is 4.0–3.5 MPa, and the pressure of the medium-pressure steam is 1.0–2.0 MPa.

[0011] The condensate temperature of the high-pressure steam ranges from 150 to 230°C, and even considering heat loss, the temperature can be above 150 to 170°C. Furthermore, the condensate quality is generally good, meeting the water injection requirements of the hydrogenation unit. By recovering this condensate through a reasonable process, and then pressurizing it with a high-pressure pump, it is injected as reaction water before the heat exchanger containing the reaction effluent or hot high-pressure gas. This ensures the water injection requirements before air cooling, effectively reduces the impact of conventional cold-state water injection on the heat load of the high-pressure heat exchanger, avoids the risk of intermittent water injection, eliminates the need for continuous water injection pipelines and valves before high-pressure air cooling, and incidentally recovers the heat from the high-temperature condensate.

[0012] The condensate temperature range of medium-pressure steam is 130–190℃. Considering heat loss, the temperature can also be above 130–170℃. The water quality is the same as that of high-pressure steam condensate, only the temperature is slightly lower. Therefore, using medium-pressure steam condensate yields similar results.

[0013] The process flow for water injection in a hydrogenation unit is further characterized in that it also includes a pre-hydrogenation section in a reforming unit.

[0014] The process flow for water injection in a hydrogenation unit is further characterized by: using high-temperature condensate as the reaction injection water after pressurization; the reaction injection water temperature is the same as that of high-pressure condensate at 150-230°C; and the reaction injection water pressure is increased by a water injection pump to a pressure higher than that of the hydrogenation reaction effluent or hot high-temperature gas fraction.

[0015] The process flow for water injection in a hydrogenation unit is further characterized in that: high-temperature condensate is continuously injected as reaction water in front of the heat exchanger of the reaction effluent or hot high-temperature gas fraction.

[0016] The process flow for water injection in a hydrogenation unit is further characterized in that: high-temperature condensate is continuously injected as reaction water in front of one or more heat exchangers of the reaction effluent or hot high-temperature gas.

[0017] The process flow for water injection in a hydrogenation unit is further characterized in that: after high-temperature condensate is continuously injected as reaction injection water in front of the reaction effluent or the high-temperature gas heat exchanger, its impact on the temperature of the hot medium is less than that of cold water injection. This hot medium can continue to provide heat to the cold medium, and its impact on the thermal balance is relatively small.

[0018] The water injection process of the hydrogenation unit described in this invention involves continuous water injection before the heat exchanger, eliminating the need for continuous water injection facilities before the high-pressure air cooler. This achieves the purpose of water injection while reducing the initial investment in the unit.

[0019] The method of the present invention has the following advantages compared with the prior art:

[0020] 1. It can minimize the impact of water injection on the heat exchange of high-pressure media and recover as much heat as possible; 2. It can avoid the risk of intermittent water injection before conventional heat exchangers.

[0021] 3. It can save on the water injection pipeline and valves in front of the high-pressure air cooler;

[0022] 4. It can also recover the heat of high-temperature condensate, reducing the overall energy consumption of the plant. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the water injection process in a conventional hydrogenation unit;

[0024] Figure 2 This is a schematic diagram of the process flow for water injection in a hydrogenation device according to the present invention.

[0025] The attached figures are labeled as follows: 1—Reaction effluent or high-temperature gas heat exchanger 1, 2—Reaction effluent or high-temperature gas heat exchanger 2, 3—High-pressure air cooler. Detailed Implementation

[0026] The following is in conjunction with the appendix Figure 1-2 Further explanation of the present invention:

[0027] The specific embodiments of the present invention will be described in detail below. The specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0028] The process flow for high-pressure medium heat extraction in conventional hydrogenation units, such as... Figure 1 As shown, the reaction effluent or hot high-pressure gas enters the high-pressure air cooler 3 after passing through heat exchangers. The reaction injection water is continuously injected before the high-pressure air cooler and intermittently injected before the heat exchanger. The intermittent injection not only affects the heat exchanger and the stability of operation, but also poses a significant risk of corrosion.

[0029] This invention provides a process flow for high-pressure medium heat extraction in a hydrogenation unit, such as... Figure 2 As shown, the reaction effluent or hot high-pressure gas sequentially enters the high-pressure air cooler 3 after heat exchange. High-temperature condensate is continuously injected before the high-pressure heat exchanger as the reaction injection water, eliminating the conventional water injection process before the air cooler. This ensures the water injection requirements before air cooling, effectively reduces the impact of conventional water injection on the heat load of the high-pressure heat exchanger, avoids the impact of intermittent water injection on production stability and potential corrosion risks, saves on high-pressure pipelines and valves for continuous water injection before the high-pressure air cooler, and incidentally recovers the heat of the high-temperature condensate.

[0030] The present invention discloses a process flow for water injection into a hydrogenation unit, applicable to the separation method of reaction effluent as either a hot high-resolution process or a cold high-resolution process. Specific Implementation Example 1:

[0032] A hydrocracking unit operates for 8400 hours annually. The reaction effluent, after heat exchange, enters a hot-high-pressure separator at 245°C. The hot high-pressure gas from the top sequentially passes through a hot high-pressure gas / mixed hydrogen heat exchanger, a hot high-pressure gas / cold low-pressure oil heat exchanger, and a hot high-pressure gas / low-temperature hot water heat exchanger, reaching a temperature of 100°C before being sent to a high-pressure air cooler for cooling. The hot high-pressure gas reaches a temperature of 171°C after passing through the first heat exchanger. If conventional 40°C intermittent water injection is used at this location, the temperature drops to 141°C after water injection, and after cooling to 100°C, 9.06 MW of heat can be recovered. If continuous injection of 170°C high-temperature condensate is used at this location, the temperature drops to 151°C, and after cooling to 100°C, 11.64 MW of heat can be recovered, 2.58 MW more than the conventional water injection process. It not only ensures the water injection effect, but also has a very considerable energy recovery, and effectively reduces the interference with production stability and the risk of intermittent water injection.

Claims

1. A process flow for water injection in a hydrogenation unit, characterized in that: In the hydrogenation unit, condensate from high-pressure steam or medium-pressure steam is used as the reaction injection water, which is continuously injected before the heat exchanger before the crystallization temperature of the reaction effluent or hot high-temperature amine salt.

2. The process flow for water injection into the hydrogenation unit according to claim 1, characterized in that: The pressure of the high-pressure steam is 4.0–3.5 MPa, and the pressure of the medium-pressure steam is 1.0–2.0 MPa.

3. The process flow for water injection into the hydrogenation unit according to claim 1, characterized in that: The condensate temperature range of the high-pressure steam is 150–230°C.

4. The process flow for water injection into the hydrogenation unit according to claim 1, characterized in that: The condensate temperature range of the medium-pressure steam is 130–190°C.

5. The process flow for water injection into the hydrogenation unit according to claim 1, characterized in that: High-temperature condensate is pressurized and used as the reaction injection water for the device; the reaction injection water temperature is 150-230℃, which is the temperature of high-pressure condensate, and the reaction injection water pressure is increased by the injection pump to a pressure higher than that of the hydrogenation reaction effluent or hot high-temperature gas fraction.

6. The process flow for water injection into the hydrogenation unit according to claim 1, characterized in that: High-temperature condensate is continuously injected as reaction injection water in front of one or more heat exchangers of the reaction effluent or hot high-temperature gas.

7. The process flow for water injection into the hydrogenation unit according to claim 1, characterized in that: This also includes the pre-hydrogenation section in the reforming unit.

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