A system and method for recycling high-temperature condensate from ethylene glycol synthesis

Abstract

The invention discloses a system and method for recycling high-temperature condensate from ethylene glycol synthesis, comprising the following steps: S1, dividing the steam condensate generated by the ethylene glycol synthesis system into two parts, one part preheating the dimethyl oxalate from the dimethyl oxalate buffer tank to a first temperature, and the other part preheating the boiler feed water to a second temperature; S2, transporting the steam condensate after preheating the dimethyl oxalate and the boiler feed water to the condensate main pipe. In the present invention, the steam condensate generated by synthesizing ethylene glycol is used to preheat the dimethyl oxalate and the boiler feed water, which, on the one hand, reduces the use of high-grade steam when 3.5MpaG steam is used to preheat the dimethyl oxalate and the boiler feed water in the prior art, increases the amount of byproducts of 0.8MPa steam, and achieves the purpose of recovering high-grade latent heat from low-grade sensible heat; on the other hand, the heat of the steam condensate is recovered in the form of material heat exchange, and the temperature of the condensate can be finally reduced, and all the heat is recovered, which is superior to the market ORC and condensate refrigeration technology, and has low investment costs and high investment returns.

Description

Technical Field

[0001] The invention belongs to the technical field of ethylene glycol preparation, and in particular relates to a system and method for recycling high-temperature condensate from ethylene glycol synthesis. Background Art

[0002] The ethylene glycol plant is equipped with three high-temperature condensate recovery units, of which the operating temperature of tank No. 2 is controlled between 155℃ and 159℃. Each unit independently processes about 330-340 tons / h of high-temperature condensate, and the total processing capacity of the three high-temperature condensate recovery units reaches 1,080 tons / h. Currently, the high-temperature condensate in tank No. 2 is used to heat the cold desalted water with an initial temperature of 40℃. After the heat exchange process, the temperature of the high-temperature condensate in tank No. 2 drops to 80℃, while the temperature of the cold desalted water rises to 118℃. The operating temperature of tank No. 3 is controlled between 109℃ and 110℃, and each high-temperature condensate recovery unit independently processes about 30-50 tons / h of high-temperature condensate, and the total processing capacity of the three units reaches 150 tons / h. The high-temperature condensate in tank No. 3 is also used to heat the cold desalted water with an initial temperature of 40℃, and after heat exchange, the condensate temperature is reduced to 57℃, and the cold desalted water is then used in the deaerator tank of the ethylene glycol plant for further heating.

[0003] The ethylene glycol condensate main pipe equipped in the ethylene glycol plant consists of three parts: the first is the high-temperature condensate - 1,080 tons of steam condensate at 80°C after the heat exchange of tank No. 2, the second is the high-temperature condensate - 150 tons of steam condensate at 57°C after the heat exchange of tank No. 3, and the third is the waste boiler steam condensate of ethylene glycol distillation, with a temperature of 90°C and a flow rate of 400 tons. After these three condensates are merged into the main pipe, the mixed temperature reaches 80°C and is sent to the desalted water station. In the desalted water station, the condensate is further cooled to 50°C~60°C through an air cooler, and then heat exchanged with production water.

[0004] The ethylene glycol synthesis unit is equipped with 12 steam drums to remove the heat of the ethylene glycol synthesis reaction. Under full load conditions, each ethylene glycol synthesis drum uses 130°C low-pressure boiler feed water with a flow rate of 19.5 tons / hour, totaling 236.4 tons / hour. The ethylene glycol synthesis reactor removes heat from the reactor through boiler feed water, and produces 0.8Map steam as a by-product.

[0005] The ethylene glycol synthesis unit is also equipped with 12 dimethyl oxalate delivery pumps, one of which is in operation and the other is on standby to ensure the stable delivery of dimethyl oxalate required for the ethylene glycol synthesis reaction. Under the designed working conditions, each delivery pump delivers 75 tons of dimethyl oxalate per hour, and the total delivery capacity of the six pumps is 450 tons per hour. The temperature of dimethyl oxalate at the outlet of the delivery pump is 88.5℃. After entering the synthesis system, it needs to be heated with 3.5Mpa steam to ensure that the temperature of dimethyl oxalate rises to above 164℃ to meet the requirements of the synthesis reaction.

[0006] See also Figure 1 , the 159℃ 1080t / h high-temperature condensate produced by the ethylene glycol synthesis unit is transported to the desalted water preheater, and at the same time, 40℃ 1080t / h cold desalted water is introduced into the desalted water preheater. The desalted water preheater is connected to the air cooler inlet through the first condensate main pipe, and the air cooler outlet is connected to the second condensate main pipe. A part of the preheated 118℃ 1080t / h desalted water is discharged, and the other part is input to the first condensate main pipe. At the same time, 90℃ 400t / h steam condensate from ethylene glycol rectification and 90℃ 150t / h steam condensate with 0.5MPa are input into the first condensate main pipe, so that the steam condensate in the first condensate main pipe is 80℃. The steam condensate in the second condensate main pipe is 40℃, and the 40℃ steam condensate can be recycled in the ethylene glycol synthesis system.

[0007] The 80°C steam condensate is sent to the downstream process section, where the air cooler is used to cool the condensate to 40°C. For this process flow, not only does it consume electricity to cool the condensate, but it also wastes the sensible heat of the condensate.

[0008] In order to solve the problem of consuming electricity to cool the condensate in the above process, condensate power generation or condensate refrigeration is used in the prior art.

[0009] Among them, condensate power generation ORC (Organic Rankine Cycle) is a technology that uses organic working fluid to continuously perform isobaric heating, adiabatic expansion, isobaric heat release and adiabatic compression in thermal equipment to convert thermal energy into mechanical energy and then generate electrical energy. Its calorific value conversion efficiency is up to 10%. The advantages of condensate power generation are:

[0010] 1. Improved energy utilization: ORC power generation can effectively utilize low-temperature waste heat resources and improve the comprehensive utilization rate of energy.

[0011] 2. Environmental protection: ORC power generation system can operate without directly consuming energy, reducing damage and pollution to the environment.

[0012] 3. Flexibility: ORC generator sets have good load adaptability and can operate stably within a wide range.

[0013] The disadvantages of condensate power generation are:

[0014] Although ORC technology is able to improve energy utilization, the energy recovery efficiency is at most 12%.

[0015] Condensate refrigeration is a technology that uses a solution-to-solution heat exchanger to refrigerate the liquid, with a maximum calorific value conversion efficiency of 52%. The advantages of condensate refrigeration are:

[0016] 1. Energy saving: Condensate absorption refrigeration can effectively utilize various low-grade thermal energy, waste gas and waste heat, thereby achieving energy saving.

[0017] 2. Environmental protection: Since it uses lithium bromide solution as the working fluid and operates under a vacuum state, it is odorless, non-toxic, and has no explosion hazard, and is considered a pollution-free refrigeration equipment.

[0018] 3. Strong adaptability: Condensate absorption refrigeration has strong adaptability to changes in external conditions and can operate stably within a wide range.

[0019] The disadvantages of condensate refrigeration are:

[0020] 1. There is a problem of low energy recovery efficiency. Summary of the invention

[0021] In order to overcome the problem of low energy recovery efficiency in the prior art, the purpose of the present invention is to provide a system and method for recycling high-temperature condensate in ethylene glycol synthesis, which can improve the energy recovery efficiency.

[0022] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0023] A method for recycling high-temperature condensate from ethylene glycol synthesis, comprising the following steps:

[0024] S1, dividing the steam condensate generated by the ethylene glycol synthesis system into two parts, one part preheating the dimethyl oxalate from the dimethyl oxalate buffer tank to a first temperature, and the other part preheating the boiler feed water to a second temperature;

[0025] S2, transports the steam condensate after preheating dimethyl oxalate and boiler feed water to the condensate main pipe.

[0026] A further improvement of the present invention is that the steam condensate after preheating dimethyl oxalate and boiler feed water includes the following steps: cooling the steam condensate after preheating dimethyl oxalate and boiler feed water, preheating the desalted water to a third temperature, and finally transporting it to the condensate main pipe.

[0027] A further improvement of the present invention is that the third temperature is 118°C; cooling the steam condensate after preheating dimethyl oxalate and boiler feed water is achieved by the following process: the steam condensate after preheating dimethyl oxalate and boiler feed water is mixed with the steam condensate from ethylene glycol distillation, so that the temperature of the steam condensate after preheating dimethyl oxalate and boiler feed water is reduced to 80°C.

[0028] A further improvement of the present invention is that the temperature of dimethyl oxalate before preheating is 88.5°C, the temperature of boiler feed water before preheating is 132°C; and the first temperature and the second temperature are 155°C.

[0029] A further improvement of the present invention is that the steam condensate after preheating the desalted water to the third temperature enters the ethylene glycol synthesis system for cyclic utilization.

[0030] A further improvement of the present invention is that the condensate temperature of the steam after preheating dimethyl oxalate and boiler feed water is 135°C.

[0031] A further improvement of the present invention is that the condensate temperature of the steam after preheating the desalted water is 40°C.

[0032] A system for recycling high-temperature condensate for ethylene glycol synthesis comprises a steam condensate storage tank, a dimethyl oxalate preheater, a boiler feed water preheater and a desalted water preheater, wherein an inlet of the dimethyl oxalate preheater is connected to an inlet of the boiler feed water preheater and a steam condensate storage tank, an outlet of the dimethyl oxalate preheater is connected to an outlet of the boiler feed water preheater and an inlet of the desalted water preheater, and the outlet of the desalted water preheater is related to a condensate main pipe.

[0033] A further improvement of the present invention is that it also comprises a desalted water heat exchanger, and the outlet of the desalted water preheater is connected to the condensate main pipe through the desalted water heat exchanger.

[0034] A further improvement of the present invention is that the outlet of the desalted water heat exchanger is connected to the ethylene glycol synthesis system via a condensate main pipe.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] In the present invention, steam condensate generated by synthetic ethylene glycol is used to preheat dimethyl oxalate and boiler feed water. On the one hand, the use of high-grade steam when 3.5MpaG steam is used to preheat dimethyl oxalate and boiler feed water in the prior art is reduced, the amount of byproducts of 0.8MPa steam is increased, and the purpose of recovering high-grade latent heat by using low-grade sensible heat is achieved. On the other hand, the heat of steam condensate is recovered in the form of material heat exchange, and the temperature of condensate can be finally reduced, and all heat can be recovered. The present invention is superior to the ORC and condensate refrigeration technologies on the market, and the investment cost is low and the return on investment is large.

[0037] Furthermore, the condensate temperature can be reduced from 80°C to 67°C, ultimately achieving sensible heat recovery of the low-temperature condensate, overcoming the problem that the sensible heat of the low-temperature condensate is difficult to recover in chemical plants.

[0038] In the system of the present invention, the boiler feed water, preheater and desalted water preheater of dimethyl oxalate preheater are arranged to exchange heat between the steam condensate in the steam condensate storage tank and the low-temperature working medium, reduce the consumption of high-grade steam to recover the heat of the condensate, and finally the heat of the condensate can be completely recovered by reducing the temperature. The heat recovery efficiency is much higher than the heat recovery efficiency on the market, and the investment is much lower than the low-grade heat recovery method on the market.

[0039] Furthermore, in the present invention, by providing a desalted water heat exchanger, the number of air coolers in operation in the rear-end section is reduced, which not only realizes heat recovery but also reduces power consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The present invention is a flow chart of steam condensate recovery in the prior art;

[0041] Figure 2 The present invention is a flow chart of the method for recycling high-temperature condensate from ethylene glycol synthesis. DETAILED DESCRIPTION

[0042] In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present invention are given in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thoroughly and comprehensively understood.

[0043] In addition, when an element in the present invention is referred to as being "fixed to" or "disposed on" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only and are not intended to be the only embodiment.

[0044] The present invention mainly utilizes the heat exchange between condensate and low-temperature working fluid to reduce the consumption of high-grade steam to recover the heat of condensate, and finally can recover all the heat of the condensate by lowering the temperature. The heat recovery efficiency is much higher than the heat recovery efficiency on the market, and the investment of this technical transformation is much lower than the low-grade heat recovery method on the market.

[0045] Example 1

[0046] The invention discloses a high-temperature condensate recycling system for ethylene glycol synthesis, comprising a steam condensate storage tank, a dimethyl oxalate preheater, a boiler feed water preheater and a desalted water preheater. The steam condensate storage tank is connected to the ethylene glycol synthesis system, the outlet of the steam condensate storage tank is divided into two paths, one path is connected to the inlet of the dimethyl oxalate preheater, and the other path is connected to the inlet of the boiler feed water preheater. The outlet of the dimethyl oxalate preheater is connected to the outlet of the boiler feed water preheater and the inlet of the desalted water preheater. The outlet of the desalted water preheater is connected to the inlet of a medium-pressure desalted water heat exchanger via a first steam condensate pipe, the outlet of the medium-pressure desalted water heat exchanger is connected to a second steam condensate pipe, and the second steam condensate pipe is connected to the ethylene glycol synthesis system.

[0047] Example 2

[0048] See also Figure 2The present invention provides a method for recycling high-temperature condensate for ethylene glycol synthesis, which redistributes and utilizes the steam condensate stored in the steam condensate storage tank after flash evaporation in the high-temperature condensate-No. 2 flash tank, and comprises the following steps:

[0049] 1. The steam condensate storage tank connected to the ethylene glycol synthesis system is divided into two parts. One part of the high-temperature condensate, the steam condensate in tank No. 2 (1080t / h of high-temperature condensate at 159°C), is used to heat the DMO (dimethyl oxalate, 88.5°C) at the outlet of the high-speed pump to the first temperature of 155°C. This is intended to reduce the use of 3.5MPa steam, thereby reducing the load of the power plant boiler. The condensate after heating DMO will flow back to the high-temperature condensate device and continue to be used to heat the cold desalted water.

[0050] 2. Another part of the high-temperature condensate, the steam condensate from the No. 2 tank, is used to heat the feed water of the ethylene glycol synthesis drum low-pressure boiler at 132°C to a second temperature of 155°C to increase the amount of 0.8MPa steam byproduct. The condensate after heating the boiler feed water is also returned to the high-temperature condensate device and combined with the condensate after heating the DMO, and is used again to heat the cold desalted water to a third temperature of 118°C.

[0051] 3. After the temperature of the condensate main pipe drops to 80°C, it is heat exchanged with 2100t / h of 40°C medium-pressure desalted water, and finally the temperature of the condensate main pipe can be reduced to 40°C, and then enter the ethylene glycol synthesis system for recycling.

[0052] The ethylene glycol project uses coal produced from Xiaobaodang No. 1 and No. 2 coal mines and Caojiatan coal mine in Yulin area in northern Shaanxi as raw material. It can also receive pulverized coke and fine coal powder produced by the coal pyrolysis device, and adopts pulverized coal gasification technology to produce synthesis gas. After the synthesis gas is transformed and purified, it is separated by H2 / CO deep cold, and the qualified CO and H2 products are sent to the DMO device and ethylene glycol device. The final product is ethylene glycol.

[0053] This technology utilizes condensate to heat dimethyl oxalate and boiler feed water, which is expected to produce an additional 12.4t / h 0.8MPaG saturated steam and save 32.7t / h 3.5MPaG saturated steam.

[0054] 0.8Mpa steam revenue:

[0055] Steam revenue 12.4×8000×81=8.03 million yuan / year;

[0056] 3.5Mpa steam revenue:

[0057] Steam revenue 32.7×8000×95=24.85 million yuan / year;

[0058] The desalted water station air cooler operates at a low load in winter and at full load in summer. The rated power of the air cooler is 37KW. The comprehensive electricity saving cost is calculated based on 20% load of the system, which can save electricity costs:

[0059] Electricity revenue 37×8000×20%×0.61×40=1.44 million / year;

[0060] In summary, the total profit of this technological transformation is 34.32 million per year.

[0061] 2. After the technical transformation of this project, 45.7 tons of steam can be saved, and it is estimated that 12.53 tons of CO2 can be reduced. Calculated based on 8,000 hours of operation per year, the annual saving of carbon dioxide is 12.53×8000=100240 tons / a.

[0062] 3. After the technical transformation of this project, 45.7 tons of steam can be saved / h, and 5.027 tons of standard coal can be saved / h. Calculated based on 8,000 hours of operation per year, the annual carbon saving is 5.02×8000=40216 tons / a.

[0063] 4. Fee Standards

[0064] 1. Steam 0.5MPa (G): 81 yuan / ton;

[0065] 2. Electricity price: 0.61 yuan / kWh;

[0066] 3. Steam 3.5MPa(G): 95 yuan / ton.

[0067] 4. 1KWh of electricity = 0.1229kg of standard coal;

[0068] 5. 1KWh of electricity = 0.5703kgCO2;

[0069] 6. 1kg standard coal = 2.493kg CO2;

[0070] 7. 1 ton of steam consumes 110 kg of coal.

[0071] The present invention has the following advantages:

[0072] 1. The sensible heat of low-temperature condensate is used to heat the process medium, reducing the use of high-grade 3.5MpaG steam and achieving the purpose of recovering high-grade latent heat with low-grade sensible heat. This is a pioneering technology in the ethylene glycol industry.

[0073] 2. The heat of condensate is recovered by material heat exchange, which can eventually reduce the temperature of condensate and recover all the heat, which is better than the ORC and condensate refrigeration technology on the market. This solution has low investment cost and high return on investment.

[0074] 3. Through the present invention, the condensate temperature can be reduced from 80°C to 67°C, and finally the sensible heat recovery of the low-temperature condensate is realized, thus overcoming the problem that the sensible heat of the low-temperature condensate is difficult to recover in chemical plants.

[0075] 4. After the implementation of this technology, the number of air coolers in operation in the back-end section can be reduced, which can not only recover heat but also reduce power consumption.

[0076] The above description is only for the best embodiment of the present invention, but it should not be understood as limiting the claims. The present invention is not limited to the above embodiments, and its specific structure is allowed to be changed. However, all changes made within the protection scope of the independent claims of the present invention are within the protection scope of the present invention.

[0077] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

Claims

1. A method for recycling high-temperature condensate from ethylene glycol synthesis, characterized in that: The following steps are involved: S1, dividing the steam condensate generated by the ethylene glycol synthesis system into two parts, one part preheating the dimethyl oxalate from the dimethyl oxalate buffer tank to a first temperature, and the other part preheating the boiler feed water to a second temperature; S2, transports the steam condensate after preheating dimethyl oxalate and boiler feed water to the condensate main pipe.

2. The method for recycling high-temperature condensate from ethylene glycol synthesis according to claim 1, characterized in that: The method comprises the following steps: cooling the steam condensate after preheating dimethyl oxalate and boiler feed water, preheating the desalted water to a third temperature, and finally conveying the condensate to a condensate main pipe.

3. The method for recycling high-temperature condensate from ethylene glycol synthesis according to claim 2, characterized in that: The third temperature is 118°C; cooling the steam condensate after preheating dimethyl oxalate and boiler feed water is achieved through the following process: mixing the steam condensate after preheating dimethyl oxalate and boiler feed water with the steam condensate from ethylene glycol distillation, so that the temperature of the steam condensate after preheating dimethyl oxalate and boiler feed water is reduced to 80°C.

4. The method for recycling high-temperature condensate from ethylene glycol synthesis according to claim 1, characterized in that: The temperature of dimethyl oxalate before preheating is 88.5°C, the temperature of boiler feed water before preheating is 132°C; the first temperature and the second temperature are 155°C.

5. The method for recycling high-temperature condensate from ethylene glycol synthesis according to claim 1, characterized in that: The steam condensate after preheating the desalted water to the third temperature enters the ethylene glycol synthesis system for recycling.

6. The method for recycling high-temperature condensate from ethylene glycol synthesis according to claim 1, characterized in that: The steam condensate temperature after preheating dimethyl oxalate and boiler feed water is 135℃.

7. The method for recycling high-temperature condensate from ethylene glycol synthesis according to claim 1, characterized in that: The condensate temperature of the steam after preheating the desalted water is 40℃.

8. A system for recycling high-temperature condensate from ethylene glycol synthesis, characterized in that: It includes a steam condensate storage tank, a dimethyl oxalate preheater, a boiler feed water preheater and a desalted water preheater. The inlet of the dimethyl oxalate preheater is connected to the inlet of the boiler feed water preheater and the steam condensate storage tank. The outlet of the dimethyl oxalate preheater is connected to the outlet of the boiler feed water preheater and the inlet of the desalted water preheater. The outlet of the desalted water preheater is related to the condensate main pipe.

9. The system for recycling high-temperature condensate from ethylene glycol synthesis according to claim 8, characterized in that: It also includes a desalted water heat exchanger, and the outlet of the desalted water preheater is connected to the condensate main pipe through the desalted water heat exchanger.

10. The system for recycling high-temperature condensate from ethylene glycol synthesis according to claim 9, characterized in that: The outlet of the desalted water heat exchanger is connected to the ethylene glycol synthesis system through the condensate main pipe.

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