KR100681240B1 - Process gas recycling system provided with exchanger using waste heat in urea plant - Google Patents

Abstract

A process gas recycling system provided with an exchanger for process piping using the waste heat in an urea plant is provided to recover heat of waste gas offered to a high pressure absorbing tub for reducing a process load applied in cooling of the high pressure absorbing tub and increasing an urea yield. A process gas recycling system provided with an exchanger for process piping using the waste heat in an urea plant includes a heat exchanger(17) for recovering waste heat mounted between a waste gas recovering pipe(19), in which carbon dioxide and ammonia of high temperature is discharged from a waste gas dissolving tower(15), and a hot water pipe(26), through which hot water is supplied from a hot water tank(24) to a water jacket(23) for heating a process pipe(21). The waste heat recovering heat exchanger transmits heat of the carbon dioxide and the ammonia in the waste gas recovering pipe into the hot water in the hot water pipe.

Description

Process gas recycling system provided with exchanger using waste heat in urea plant}

1 is a block diagram of a conventional urea synthesis process,

2 is a block diagram showing a conventional process gas recovery facility for recovering the waste gas generated in the melamine manufacturing process as raw materials together with the unreacted gas in the urea plant,

3 is a configuration diagram showing a process gas recovery facility of the urea plant according to the present invention,

4 is a view showing a state in which the warm water heated by the heat exchanger of the present invention is supplied to the jacket of the process pipe.

<Explanation of symbols for the main parts of the drawings>

10: synthesis tower 11: high pressure decomposition tower

13: high pressure absorption tank 14: pump

15: waste gas cracking tower 17: heat exchanger for waste heat recovery

21: process piping 22: pipe

23: water jacket 24: thermal water tank

25: water pump 26: thermal water pipe

The present invention relates to a process gas recovery facility of an urea plant having a heat exchanger for process piping thermal insulation using waste heat, and more particularly, waste gas in an urea plant in a recovery process for reusing waste gas generated during the production of melamine as a raw material of urea. By further comprising a waste heat recovery heat exchanger used to recover the heat of the waste gas moving from the decomposition tower to the high pressure absorption tank to heat the warm water of the water jacket for the process pipe insulation, the heat of the waste gas provided to the high pressure absorption tank is recovered. As a result, it is possible to reduce the process load for cooling in the high pressure absorption tank, to increase the production of urea by reducing the process load, and to reduce the input amount of steam supplemented with the heat source of the existing warm water. Urea plant with heat exchanger for process piping insulation using waste heat It relates to a process gas recovery equipment.

In general, the elements can be synthesized in a number of ways, but the synthesis method that is currently used the most is to go through the process of FIG.

That is, when ammonium carbonate (NH ₄ CO ₂ NH ₂ ) is synthesized by reacting carbon dioxide (CO ₂ ) and ammonia (NH ₃ ) as source gas, ammonium carbonate is converted into water (H ₂ O) and urea (NH ₂ CONH ₂ ). It is decomposed and the liquid urea is processed into a urea product through crystallization, drying and granulation.

Unreacted carbon dioxide and ammonia not converted to urea in the synthesis process can be recovered and used again in the synthesis process.

Meanwhile, in the urea manufacturing process described above, as shown in FIG. 1, waste gas is discharged while the liquid urea passes through the crystallization, drying, and granulation steps, and carbon dioxide and ammonia, which are reaction by-products, are also produced in the production of melamine using urea. The containing waste gas is discharged.

Such waste gas is conventionally discharged into the atmosphere, but if it is just released into the atmosphere, there is a problem of odor generation and air pollution. Especially, since waste gas contains carbon dioxide and ammonia, which are raw materials of urea, There is a loss.

Therefore, the discharge of waste gas into the air is regulated, and a method is known in which carbon dioxide and ammonia in waste gas are absorbed in water (absorption liquid), collected, recovered, and used as raw materials together with unreacted gas.

Figure 2 shows a conventional process gas recovery facility for recovering the waste gas generated in the melamine manufacturing process as a raw material together with the unreacted gas in the urea plant, as follows.

In a urea manufacturing plant (hereinafter referred to as urea plant), when carbon dioxide and ammonia are supplied into the synthesis column 10 as raw materials, these raw materials react in the synthesis column 10 to be synthesized into urea, and then urea is converted into urea. The unreacted gas, that is, unconverted, is sent to the autoclave 11 together with carbon dioxide and ammonia.

In the autoclave 11, thermal energy is provided to decompose by the heating means 12, and unreacted carbon dioxide and ammonia are separated from urea, where unreacted gases of carbon dioxide and ammonia are separated. The urea is completely separated from the unreacted gas through a low pressure cracking tower (not shown) and an atmospheric pressure cracking tower (not shown), and then sent to a post process such as a crystallization process.

On the other hand, carbon dioxide and ammonia separated from the urea are sent to the high pressure absorption tank 13 through the unreacted gas recovery pipe 18 installed between the high pressure decomposition tower 11 and the high pressure absorption tank 13, The water is absorbed in the absorption tank 13 and then sent back to the synthesis column 10 by the pump 14 to be reused as a raw material of the urea.

As described above, the synthesis tower 10 synthesizes the urea using the newly supplied raw materials and the recovered raw materials. As described above, the urea separated from the unreacted gas through the decomposition tower 11 is subjected to a post-process. It is either finished with urea or sent to a melamine manufacturing plant for the production of melamine.

Meanwhile, in a melamine manufacturing plant (melamine plant), urea is supplied from an adjacent urea plant to produce melamine from urea. During the melamine manufacturing process, waste gas including carbon dioxide and ammonia, which are reaction by-products, are generated.

This waste gas contains carbon dioxide and ammonia, which can be used as raw materials for urea. The carbon dioxide and ammonia in this waste gas is absorbed and collected in water (absorbent) for reuse as urea raw materials, and then the waste gas cracking tower of the urea plant. Will be sent to (15).

When carbon dioxide and ammonia are absorbed in water and sent to the waste gas cracking tower 15 of the urea plant as described above, thermal energy is provided in the waste gas cracking tower 15 so that decomposition can be caused by the heating means 16. At the same time, the waste gases carbon dioxide and ammonia are again separated from the water.

Here, the waste gas of carbon dioxide and ammonia separated from the water becomes the same component as the unreacted gas from the high pressure decomposition tower (11).

The carbon dioxide and ammonia separated from the water in the waste gas cracking tower 15 as described above is introduced into the unreacted gas recovery pipe 18 through the waste gas recovery pipe 19 and the unreacted carbon dioxide from the high pressure cracking tower 11. And it is combined with ammonia, and then sent back to the synthesis tower 10 through a high pressure absorption tank 13 is reused as a raw material of the urea.

In this way, the urea plant separates the synthesized urea from unreacted carbon dioxide and ammonia, and also separates carbon dioxide and ammonia from the waste gas absorption solution (carbon dioxide + ammonia + water) sent from the melamine plant, and collects the separated carbon dioxide and ammonia together. It is provided with a facility for sending to the high pressure absorption tank 13 to be absorbed in water and then recovered to the synthesis column 10 for use as a raw material of the urea.

However, sufficient thermal energy is required to separate carbon dioxide and ammonia from the high pressure cracking tower 11 and the waste gas cracking tower 15, so that each cracking column 11 and 15 may be decomposed as described above. Separate heating means 12, 16 for applying heat are provided.

In addition, process gases, that is, carbon dioxide and ammonia, which are sent after decomposition in each decomposition tower 11 and 15 of the urea plant are absorbed by water in the absorption tank 13 and reused as raw materials for urea, but decomposed at high temperature for reuse. When carbon dioxide and ammonia are absorbed into the water in the absorption tank 13, an exothermic reaction is required and cooling is necessary again.

To this end, the absorption tank 13 is provided with a separate cooling means (not shown) for cooling the heat generated when absorbed by water with cooling water.

Therefore, in the process gas recovery facility of the urea plant made as described above, in the process of applying heat in the cracking tower and cooling again in the absorption tank 13, not only the size of the required device is increased but also energy is used for decomposition and the energy used is There is a problem that a double loss of energy occurs such as consumed by the cooling water.

In addition, since a large process load is applied to the cooling in the absorption tank, the operation load of the entire plant is greatly limited, and the production of urea is also greatly affected.

In fact, in summer, as the temperature of the cooling water rises (27 ° C. to 30 ° C.), the process load is lowered compared to the winter season.

In particular, when the waste gas generated in the melamine manufacturing process was not recovered and reused, the process was needed only for the unreacted gas from the high-pressure cracking tower, so the process load for cooling did not act as a big problem. Cooling is also required for the high temperature waste gas sent from the waste gas cracking tower as it is recovered and reused, and further increase in process load and increase in device size have been pointed out as big problems.

Therefore, the present invention was invented to solve the above problems, the heat of the waste gas moving from the waste gas decomposition tower in the urea plant to the high pressure absorption tank in the recovery process for reusing the waste gas generated during the production of melamine as raw material of the urea. Is further provided with a waste heat recovery heat exchanger used to heat the warm water of the water pipe for the process pipe insulation to recover the heat, the process is taken when cooling in the high pressure absorption tank as the heat of the waste gas provided to the high pressure absorption tank is recovered It is possible to reduce the load, increase the production of urea by reducing the process load, and elements having a heat exchanger for heat treatment of process piping using waste heat, which has the advantage of reducing the input amount of steam supplemented with the heat source of the existing warm water. The purpose is to provide a process gas recovery facility for the plant.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

The present invention provides a high pressure decomposition tower for separating carbon dioxide and ammonia, which are unreacted gases after urea synthesis, and unreacted gas recovered from the high pressure decomposition tower through a pipe for recovering unreacted gas as raw material of urea. A high pressure absorption tank for absorbing water and a waste gas decomposition tower for recovering carbon dioxide and ammonia from waste gas generated from the melamine plant in a state of being absorbed in water and separating carbon dioxide and ammonia from the waste gas recovery pipe to the high pressure absorption tank. In the process gas recovery equipment of the urea plant,

The waste gas recovery pipe is installed between the waste gas recovery pipe through which hot carbon dioxide and ammonia are discharged from the waste gas decomposition tower, and the warm water pipe connected to the warm water jacket for the process pipe insulation from the warm water tank. Process gas of the urea plant having a heat exchanger for heat treatment process pipe using waste heat, characterized in that further comprising a heat exchanger for waste heat recovery configured to transfer heat of carbon dioxide and ammonia in the receiving pipe to the warm water in the water pipe It is characteristic of the recovery facility.

In a preferred embodiment, the warm water pipe is installed heat exchanger for waste heat recovery, characterized in that the warm water pipe connected to the water jacket for the process piping of the crystallization process in the urea plant.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

The present invention relates to a process gas recovery facility of an urea plant having a heat exchanger for process piping thermal insulation using waste heat, wherein the high pressure from the waste gas cracking tower in the urea plant in a recovery process for reusing waste gas generated at the time of melamine production as urea raw material. The main feature is to further include a separate heat exchanger for recovering the heat of the waste gas moving to the absorption tank.

Figure 3 is a block diagram showing a process gas recovery equipment of the urea plant according to the present invention, Figure 4 is a view showing a state in which the warm water heated by the heat exchanger of the present invention is supplied to the water jacket of the process pipe.

In the present invention, the composition tower 10, the high pressure decomposition tower 11, the high pressure absorption tank 13, the waste gas decomposition tower 15 and the like, the function and role are the same as in the prior art.

First, as shown in Fig. 3, in the recovery facility of the present invention, a heat exchanger 17 for recovering heat of the waste gas is further provided.

Waste gas generated during melamine manufacturing process, namely carbon dioxide and ammonia, is absorbed into water and sent to the waste gas decomposing tower 15 of the urea plant. The waste gas decomposing tower 15 separates carbon dioxide and ammonia from the water. Heat is applied.

The carbon dioxide and ammonia separated from the water are sent to the high pressure absorber 13 at a high temperature and cooled by the cooling water to be absorbed by the water, and then to be used as a raw material of the urea in the absorbed water. 10) are sent to.

The heat applied in the waste gas cracking tower 15 is heat necessary to separate carbon dioxide and ammonia from water, but the carbon dioxide and ammonia sent to the high pressure absorption tank 13 are cooled by the cooling water to be absorbed by the water again. The heat moving to the high pressure absorption tank 13 together with carbon dioxide and ammonia becomes waste heat that should be absorbed by the cooling water, and this waste heat has conventionally caused an increase in the process load (cooling load) in the high pressure absorption tank 13. .

Therefore, in order to lower the process load in the high pressure absorption tank 13, it may be considered to recover the waste heat sent to the high pressure absorption tank 13 by the waste gas, in the present invention high pressure together with carbon dioxide and ammonia In order to recover the waste heat moving to the absorption tank 13, a heat exchanger 17 is additionally installed. The waste heat is recovered by the heat exchanger 17 to be used for the insulation of the process pipe 21. It is a feature of the present invention.

Usually, in the urea plant, in order to prevent the urea from solidifying in the crystallization step, all the pipes 21 of the crystallization step are provided with a water jacket 23 for pipe insulation.

That is, the water jacket 23 surrounding the pipe 21 through which the urea flows is provided, and hot water, that is, warm water, flows into the water jacket 23 so that the warm water is allowed to flow. The temperature of the elements flowing in the pipe 21 is prevented from dropping and some heat is provided to prevent the elements from hardening.

The conventional process pipe insulation system, as shown in Figure 3, so that the thermal water is stored in the warm water tank 24, and the warm water flows through it to provide heat of the warm water to the elements in the process pipe 21 The water jacket 23 installed in the process pipe 21 and the warm water tank 24 and the water jacket 23 to allow the warm water stored in the warm water tank 24 to flow into and out of the water jacket 23. A thermal water pipe (26) connected between the insulated water inlet (22a) and the outlet (22b), respectively, and the thermal water tank (24) and the water jacket (23) provided on the thermal water pipe (26). It comprises a water pump 25 to provide a pumping force to circulate the warm water between.

In such a process pipe insulation system, the warm water tank 24 is continuously supplied with high temperature warm water (steam or condensate) from the outside to provide heat to the elements in the process pipe 21 through the water jacket 23. do.

Figure 4 shows the general shape of the water jacket 23 is installed around the process pipe 21, and as shown in the usual pipe 21 of the crystallization process that requires the insulation of the separate pipe 22 through which warm water flows. It is installed so as to surround the double pipe form, and the water jacket 23 is configured to allow the warm water flowing in and out through the inlet 22a and the outlet 22b on the other side inside the separate tube 22 flows. .

As described above, the surroundings of the process pipe 21 are jacketed with warm water to insulate the process pipe 21 and the internal elements, thereby preventing the elements from hardening.

In the present invention, the warm water pipe 26 and the carbon dioxide and ammonia from the waste gas decomposition tower 15 are installed to connect the warm water to the water jacket 23 of the process pipe 21 from the warm water tank 24. A waste heat recovery heat exchanger (17) is installed to allow heat exchange between the waste gas recovery pipes (connected from the waste gas cracking tower to the unreacted gas recovery pipes) 19 so as to move to the high pressure absorption tank 13. do.

The waste heat recovery heat exchanger (17) is for heating the warm water circulated for warming of the process pipe (21) using waste heat of the waste gas (carbon dioxide and ammonia) from the waste gas decomposition tower (15). It is provided to exchange heat between the warm water flowing along the pipe 26 and the waste gas moving along the waste gas collection pipe 19 to transfer heat of the waste gas to the warm water.

The waste heat recovery heat exchanger 17 may be implemented in the form of various heat exchangers commonly known to those skilled in the art. For example, insulated water passes through the inside of a shell, and the heat exchanger may be heat-exchanged inside the shell. The waste gas may be configured to pass therethrough.

Referring to FIG. 3, the waste gas at 130 ° C. from the waste gas decomposition tower 15 is deprived of heat while passing through the heat exchanger 17, and is recovered to the high pressure absorption tank 13 in a state where the temperature is lowered to 90 ° C. The heat passing through the heat exchanger 17 can be seen that the heat of the waste gas is heated to 75 ℃ 80 ℃ and then supplied to the water jacket 23 of the process pipe (21).

In addition, the warm water introduced into the water jacket 23 of the process pipe 21 keeps the process pipe 21 to prevent the elements in the process pipe 21 from hardening, and the heat water deprived of heat in this process is It can be seen that after being recovered to the warm water tank 24 is recycled.

As described above, by installing the heat exchanger 17 for waste heat recovery to transfer the heat of the waste gas to the warm water, it is possible to lower the temperature of the waste gas that is moved to the high pressure absorbing tank 13, and as a high pressure absorbing tank 13, As a small amount of heat is provided through the waste gas, it is possible to reduce the process load on cooling in the high pressure absorber (13).

In this way, when the process load in the high pressure absorbing tank 13 is reduced, it is possible to increase the production of urea with the same size equipment.

In addition, since the waste heat recovery heat exchanger 17 recovers waste heat and provides it to the warm water, there is also an advantage of reducing the input amount of steam supplemented with the heat source of the existing warm water.

As described above, the heat of the waste gas moving from the waste gas decomposition tower in the urea plant to the high pressure absorption tank in the recovery process for reusing the waste gas generated during the production of melamine for process pipe insulation using waste heat according to the present invention as the raw material of the urea. Is further provided with a waste heat recovery heat exchanger used to heat the warm water of the water pipe for the process pipe insulation to recover the heat, the process is taken when cooling in the high pressure absorption tank as the heat of the waste gas provided to the high pressure absorption tank is recovered It is possible to reduce the load, increase the yield of urea by reducing the process load, and also provide the advantage of reducing the input of steam supplemented with the heat source of the existing warm water.

Claims (2)

High pressure absorption tower to separate carbon dioxide and ammonia, which are unreacted gases after urea synthesis, and water to recover unreacted gases recovered from the high pressure decomposition tower through unrecovered piping as raw materials for urea. And a waste gas cracking tower for receiving carbon dioxide and ammonia of the waste gas generated from the melamine plant as absorbed in water and separating carbon dioxide and ammonia therefrom and recovering the waste gas to the high pressure absorption tank through a waste gas recovery pipe. In the process gas recovery equipment, The waste gas recovery pipe is installed between the waste gas recovery pipe through which hot carbon dioxide and ammonia are discharged from the waste gas decomposition tower, and the warm water pipe connected to the warm water jacket for the process pipe insulation from the warm water tank. Process gas of the urea plant having a heat exchanger for heat treatment process pipe using waste heat, characterized in that further comprising a heat exchanger for waste heat recovery configured to transfer heat of carbon dioxide and ammonia in the receiving pipe to the warm water in the water pipe Recovery equipment. The method according to claim 1, Process gas recovery of the urea plant having a heat exchanger for the process pipe insulation using waste heat, characterized in that the heat-insulating pipe is installed heat exchanger for the waste heat recovery is connected to the water jacket for the process piping of the water purification process in the urea plant. equipment.

Images