JPS61167424A - Process for separating and recovering steam mixed with water-insoluble gas - Google Patents

Abstract

PURPOSE:To recover steam having specified pressure without using a heat exchanger nor increasing power consumption of compressor for elevating pressure by causing adiabatic autovaporization of circulating water which has been heated by contacting directly with steam-contg. gas, in an evaporative cooler under reduced pressure, and elevating the pressure thereafter. CONSTITUTION:Steam contg. inactive gas for water is introduced into a condenser heater 1 through an inlet 2 for the initial gas, and circulating water, on one hand, cooled to a specified temp. by an evaporative cooler 10 is sprayed from a liquid dispersing nozzle 4 to contact the gas with liquid on a packing material 5. The sensible heat held by the initial gas and the latent heat of condensation of the steam are transferred to the circulating water, and the gas itself is cooled and dehumidified, and the circulating water is heated. This hot water is sprayed from a nozzle 11 by transporting to the evaporative cooler 10 set to a reduced pressure by the suction of a steam compressor C. The circulating water is cooled adiabatically to a temp. corresponding to its pressure by autovaporization. Generated steam is recovered by elevating the pressure to a specified value by the steam compressor C. The cooled circulating water is transported to the nozzle 4 with a pump P2.

Description

[Detailed Description of the Invention] (a) Industrial Application Field The invention of B is a chemical industry in which a large amount of steam is mixed in a raw material system to perform a gas phase reaction, and the water vapor contained in the reaction product gas is separated. The present invention relates to energy-saving technology for separating and recovering water vapor contained in exhaust gas generated from drying processes in fields such as chemistry, paper manufacturing, and the food industry.

(Middle) Conventional technology Pass the reaction product gas or dry exhaust gas as described above through a heat exchanger attached to a water evaporator, condense the contained water vapor, and heat and boil the water on the other side via the heat transfer surface. The usual method is to obtain water vapor by

In this case, it is customary to set the water temperature on the evaporation side to be lower than the condensation end temperature by the temperature difference necessary for heat transfer.

In addition, these reaction gases or dry exhaust gases are transferred to a bubble column,
The water vapor in the gas is condensed by direct contact with the circulating water through a packed tower, etc. At that time, the circulating water is mainly heated and heated using the latent heat of condensation, and the obtained hot water is evaporated in the same manner as in the previous example. Attempts have also been made to generate steam by sending water to a liquid-liquid heat exchanger attached to the heat exchanger and heating and boiling the water on the other side via a heat transfer surface, while also returning the circulating water that has left the heat exchanger to its original source. ing.

(c) Problems to be Solved by the Invention In the former example of the conventional techniques, a temperature difference between the heat transfer surface and the heat transfer is required between the raw gas and the evaporated water. As the content of non-condensable components in the raw gas increases, the heat transfer coefficient (Ka2g/?F1'', '0.11) on the gas side at the heat exchanger heat transfer surface decreases significantly, resulting in a large heat transfer area. equipment costs will increase.

In addition, if we create a large temperature difference across the heat transfer surface to avoid this, the boiling temperature of water and, as a result, the vapor pressure will further decrease, which will further increase the power of the compressor to recover steam at a given pressure. There are drawbacks such as:

In the latter example, there is no heat transfer surface for heat exchange between the raw gas and the boiling water, and the gas-liquid contact surface itself can fulfill its role in bubble columns and packed towers. There is an advantage in being able to provide The amount of heat from the hot water that has been extracted must be transferred to the water on the evaporator side via a heat exchanger.
creates the same expensive heat exchanger problem as in the former example,
As in the previous example, this and the compressor power have a reciprocal relationship.

Furthermore, in order to improve the heat transfer coefficient of such a liquid-liquid heat exchanger, forced circulation is required on both sides, which naturally requires equipment costs and power costs for pumps.

This invention solves the problem that conventional technology has, namely that the equipment cost is high due to the use of a heat exchanger, and when trying to alleviate this, the temperature difference on the heat transfer surface becomes large, and low boiling point water vapor is transferred to the required pressure. The purpose of this project is to resolve the contradiction that increases the power cost of a compressor that pressurizes the air.

B) Means and operation for solving the problems This invention will be explained with reference to the drawings. In FIG. 1, water vapor containing gas insoluble in water is sent from a raw gas source 2 to the lower part of a condensing heater body 1. On the other hand, the circulating water cooled to a predetermined temperature by the evaporative cooler is sent by the pump P2 to the liquid dispersion nozzle 4 provided at the upper part of the filling part 5, and is uniformly distributed on the upper surface of the filling part 5. 5 consists of a filling and a support frame that supports it, raw gas passes through 5 from the bottom to the top, and circulating water passes from the top to the bottom.

The packing material is generally one used in an absorption column or a distillation column.It is desirable that the packing material filled per unit volume has a large surface area and that the pressure loss caused by passage of the raw gas is small. Commercially available products such as Ball Rings, Interlocks, Terrarets etc. are suitable for this purpose.

Furthermore, depending on the temperature and components of the raw gas, it is necessary to select a heat-resistant and corrosion-resistant material.

Known techniques are used to wet the surface of the filling as uniformly as possible with the falling water, and gas containing a large amount of high-temperature water vapor passes through it, so the sensible heat of the gas is proportional to the gas temperature and the water concentration on the surface. It moves to the water using the temperature difference between it and the water as a driving force.

Further, while the water vapor partial pressure in the gas is higher than the water vapor pressure exhibited by the water temperature, the water vapor moves to the surface of the water and condenses using this differential pressure as a driving force. In other words, the latent heat possessed by the raw gas moves to the water side. On the large gas-liquid contact surface constructed around the packing in this way, a predetermined amount of sensible heat and latent heat possessed by the raw gas is transferred to the descending circulating water. In this way, the gas itself is cooled and dehumidified, and the circulating water is heated and collected in a liquid reservoir 6 provided at the bottom of the tank 5.

The raw gas thus reaches a predetermined temperature and is discharged from the raw gas outlet 3 while still containing saturated steam and the entire amount of water-insoluble gas. Next, the hot water collected in the tank 6 is irrigated into the filling part 12 by a pump P1 and a liquid dispersion nozzle 11 provided at the upper part of the evaporative cooler body 1°. Like 5 above, this filling part provides a large wetted area within the space, and the circulating water falls into the liquid reservoir 16 at the bottom of 10 while wetting this surface. The internal pressure of No. 10 is suctioned by vapor compressor C and set lower than the internal pressure of No. 1, and the circulating water is adiabatically cooled by self-evaporation to a water temperature corresponding to the pressure. The discharge pressure of C is determined by the required pressure of recovered steam, but the required power of the compressor increases as the compression ratio (discharge pressure/suction pressure) increases. The thus cooled circulating water is pumped out from 16 by pump P2 and sent to 4 again.

In this way, a predetermined amount of water vapor contained in the raw gas 2 is condensed and evaporated using the circulating water, and is finally recovered as steam on the discharge side of C. The water balance varies depending on the operating conditions, sometimes requiring the addition of water to the entire system and other times requiring removal of water from the system.

The present invention is also effective when the raw gas contains a component composition such as a hydrocarbon-based low-boiling liquid that is insoluble in water and will condense together under conditions where water condenses.

In that case, the liquid collected at the bottom 6 of 1 is led to a separately provided decanter (not shown), separated into an aqueous phase and an oil phase, and only the aqueous phase is sent to 11 using Pl. Bye. The separated oil phase shall be sent to an appropriate treatment. Example 1 is an example in which the present invention was applied to a process for producing styrene from ethylbenzene.

In this case, when the raw gas starts to be cooled, initially only water vapor continues, and then both water vapor and oil condense. Therefore, this can be achieved by increasing the steam recovery rate, but in this example, the operating conditions are limited to a range where only water vapor condenses.

Next, a method will be described in which this invention can be economically applied even when the temperature difference between the raw gas population 2 and the outlet 3 is small PGM in FIG.

As shown in Example 1, the temperature of the circulating water relative to the inlet and outlet gas temperatures is usually around 2°C, and sometimes 1'
Sufficient enthalpy can be transferred even below O.

On the other hand, as mentioned above, the power of the compressor is controlled by the compression ratio of the vapor passing through it, so if the raw gas outlet gas temperature is lowered significantly compared to the inlet gas temperature in order to increase the enthalpy recovery rate from the raw gas, it will be commensurate with that. This results in a contradiction in that the temperature of the circulating water supplied to the condenser, that is, the boiling point in the cooler, decreases, resulting in a decrease in the suction pressure of the compressor, an increase in power, and a loss of economic efficiency.

FIG. 2 is a flow sheet suitable for such a case. Inside the condenser 1, filling parts 8.5 are provided in two stages, upper and lower, and an upper stage liquid reservoir 7 and a lower stage liquid dispersion nozzle 4 are arranged in the middle. As in FIG. 1, the raw gas enters the bottom of 1 through 2 and, while passing through 5, comes into contact with the circulating water from 4 to perform enthalpy exchange. Subsequently, it passes through 8 through the opening of 7, where it exchanges enthalpy with the circulating water from 9 as in the lower stage, and then exits the strand 3.

On the other hand, the heated circulating water undergoes different treatments in the lower and upper stages. First, the hot water discharged from the lower stage 6 passes through 11.12, self-evaporates and cools down to a predetermined temperature, as shown in Figure 1, and then passes through 13 to the atmospheric leg receiver 14, where it reaches 4 by Pl.
On the other hand, the vapor compressor C1 sucks in all the steam generated at a pressure corresponding to the temperature of step 13 and recovers steam at a predetermined pressure.

Similarly, the hot water collected in the upper stage 7 is sent to an evaporative cooler 17 provided separately from 10, and is cooled to a predetermined temperature through 16.17, and then returns to 9 through 18.19 and P2.

At this time, the vapor compressor C2 sucks water vapor under a vapor pressure commensurate with the temperature of the circulating water collected at 18, and obtains steam at a predetermined pressure, similar to C1. The flow sheet in Figure 2 shows 1 at approximately atmospheric pressure, so 10
, 15 are operated under reduced pressure, and in order to send the hot water from 10.7 to 11.16, the relative height of the equipment group is set according to the pressure conditions. No need for a pump. Therefore, one circulating water pump may be installed for each filling section. Note that this flow sheet does not show lines for supplying or discharging water according to the increase or decrease of circulating water, as in FIG. 1, but this may be determined as appropriate depending on the operating conditions. In addition, in Fig. 2, two filling sections (5.8 and 5.8) were provided inside the condenser 1, and the gas flow was made in series between them, and the circulating water flow was made independent of each other, but the tower itself was divided into two. It is also possible to connect each group separately. Conversely, it is also possible to design a system in which the coolers 10.15 are combined into one and a partition is provided inside to separately control the internal pressure.

By providing two sets of condensers and coolers in this manner, the suction pressures of the compressors C1 and C2 are controlled by the temperature of the circulating water returned to the respective filling sections. Therefore, the suction pressure to cl is higher than the pressure to C2, and the power consumption of C1 is reduced accordingly. The greater the temperature difference between the inlet and outlet of the raw gas, the more economical it becomes to install two such sets, and if necessary, it is desirable to connect more condensing systems in series with the gas flow. . Example 2 is an example in which the present invention is applied to increase the recovery rate of the enthalpy possessed by such raw gas.

(e) Effects of the Invention As explained above, this invention uses an expensive heat exchanger to convert water vapor that mixes with gases that are insoluble in water, that is, water vapor that normally could only be discarded or used only to produce hot water. This opens the door to recovering most of the steam without using it and using it as steam at a predetermined pressure.

In addition, since a direct contact method is adopted between the raw gas and the circulating water in the filling section for heat recovery, the temperature level of the circulating water can be kept higher than in the heat exchange method, and the pressure on the suction side of the vapor compressor is increased. can be made higher, which leads to a reduction in the compression ratio and, in turn, to a reduction in power.

In particular, in order to utilize the enthalpy of the raw gas as much as possible and increase the steam recovery rate, it is possible to further reduce power consumption by providing a plurality of sets of condensing heaters and evaporative coolers.

Example 1 When synthesizing styrene monomer by dehydrogenating ethylbenzene by gas-phase catalytic reaction, it is customary to mix a large amount of water vapor with the raw fiber to improve the reaction yield and prevent clogging of the equipment by by-products. It is.

This reaction product gas is at a high temperature and is normally led to a waste heat boiler to cool it down to about 160°C, and the sensible heat during that time is recovered as steam, but after that it is passed through an air-cooled or water-cooled heat exchanger. Most of the water vapor and reactants contained in the gas are condensed and separated from insoluble gases such as hydrogen, and the resulting condensate is sent to the next process.

Although a large amount of heat is exchanged during this process, it is not industrially possible to recover this as steam and use it to dilute the raw gas.

The reaction product gas (raw gas) leaving the waste heat boiler in this way
The present invention is applied to the following conditions under the conditions shown in Table 1.

Table 1 Raw gas composition and operating conditions Gas composition; Moisture ・・・・・・・・・・・・・・・
s7, q2% mol hydrogen...
・・・・・・・・・・・・ 4.61 Benzene・・・・・・・・・ 0.12 Toluene・・・・・・・・・
・・ 0.08 Ethylbenzene ・ 2.61 Styrene ・・・・・ 4.61 Others ・・ 0.05 Total ・
・Song... 100.00 Gas pressure; Condensing heater inlet Normal pressure gas temperature; Raw gas 160 °C Condensing heater inlet 96.6'0 Condensing heater outlet 92.0°0 Circulating water temperature; Condenser inlet temperature 90.0°0 Condensation Condensation outlet degree 95.0°C Compressor pressure; Suction side 0.71 Kf/7 a
4i discharge side 2.02Kp/-α6 raw gas is a mixed gas containing a large amount of water vapor, hydrogen, and aromatic hydrocarbons at normal pressure and 160°C as shown in Table 1. First, when water is brought into adiabatic contact with the gas to cause an isenthalpic change, the gas reaches saturation at a wet bulb temperature of 96.6°C. Next, if heat is removed from this gas from the outside, the gas temperature will drop, and moisture will condense accordingly. Gas temperature 89°9°C
When the temperature is lowered below, aromatic components begin to condense. The condensed liquid at this time is poorly soluble in water and separates into two phases from the condensed water as an oil component.

Table 2 shows the amount of heat that must be removed (or the amount of heat that can be recovered) for each temperature while continuing such gas cooling.

As can be seen from this table, initially, even if the temperature drop from the wet bulb temperature of 96.6°0 is relatively small, the amount of condensation is large and the heat recovery rate is high, but as the heat recovery rate is gradually increased, Requires large temperature drop.

Table 3 shows the results obtained under the operating conditions shown in Table 1 according to FIG.

As described above, according to the method of the present invention, the enthalpy at the reactor outlet is 55 cm, and the amount of water vapor contained is 67.9%, at 2~/c1.
Saturated steam of i1.120'O can be recovered and returned to the inlet of the reactor, and the amount of steam supplied from the outside can be reduced to about 100%.

Table 2 Recoverable heat of styrene reaction product gas Styrene I in the raw gas per Kmo13 Table 3 Operating conditions and results for steam recovery Styrene I in the raw gas Kmo-4?
water evaporation temperature/pressure crab 90°a10. y1Ky/a
ir air recovery recovery steam temperature normal pressure crab 10'
O/2.02 K9/Shoulder aJi Evaporation water amount: 2t1. B
Kp Compressor moving crab theory 11.7KwH Shaft power 19.5 BKWH (compressor efficiency 60%) Actual power 20.5 KWH (Mo 1 - efficiency 95%) Amount of steam generated: 255.4Ky Same enthalpy = 1.427 X 105KJ Generated steam enthalpy/total enthalpy of raw gas: ss, o
%Used power/generated sum: 87.8 KWH/
TON Example 2 The present invention is applied to the evaporated moisture generated in a paper dryer in a paper mill and recovered, and the resulting steam is sent to the heating cylinder again and used for drying.

There are usually several dozen rotating cylinders inside the dryer, and steam of about 3 to 1.5 KP/- is introduced into each of them to appropriately heat the surface of the cylinders. The paper containing moisture passes through the cylinder while being in contact with the surface of the cylinder, where it is heated and dried.

Due to paper quality and energy saving considerations, the surface temperature of each cylinder is not constant and is divided into several different groups.

The drying zone has a semi-sealed structure with a hood surrounding it, and the generated steam is carried out of the hood along with air entering from the outside by an exhaust fan. Therefore, this exhaust gas contains a large amount of air, and in many cases the temperature drops to around 80°C, making it difficult to recover steam from this point, and there is no example that has been realized yet.The present invention is implemented in this system. In order to do this, the drying zone must first be sealed, and the minimum opening should be provided at the entrance and exit of the paper, and when the generated steam is sucked out of the zone with a blower, air from the outside can be drawn into the hood. To minimize leakage, it is necessary to adjust the pressure in the zone to maintain it slightly below atmospheric pressure. If you take this into account, the air contained in the generated steam away from the hood will be 10~
15 inch volume, its dew point temperature can be stopped at 97~95'08K. Steam containing such a water-insoluble gas is first sent to a system as shown in FIG. 2, and the operation as described above is carried out. The operating conditions and their expected results are shown in Tables 4 and 5, respectively. Note that the numbers in parentheses below are the same as the numbers shown in FIG. 2 and indicate each point. Also, heat loss in each part is ignored.

Table 4 Operating conditions for steam recovery in a paper dryer Air mixing rate in raw gas: 15.5% Gas temperature: Raw gas +21 96.0 '0 Midpoint between both light filling parts 92. O゛C! Gas generation (3) an, o ゛c circulating water temperature: (
6), αυ point 94. o''C diagonal, α slope, (4) point 90.5'0 (7), (m (0 point 90.0'0 eel, down ■, (9) point 78.5°C Compressor pressure Crab C1 suction side 0.73 Kf/cd a4i
Discharge side 3.00 K9/7 aA, lC2 suction side
0.45 Kf/lyd a4i discharge side 1-80
Kp/7 aA, aTable 5 Expected operating results The following are raw gas I Kmo#, that is, water vapor mixed into it 15. The value per sKp is shown.

Amount of evaporation from each evaporative cooling can: From α1 s, 5Ky0
From 9 s, 1Ky total 13.6 Dynamic crab theory of compressor C1 0.67KWH shaft power 1.1
1KWH (compressor efficiency 60%) Actual power 1, 17 KW
Dynamic crab theory of H (%-ter efficiency 95%) compressor C2 0
．． 38KWH shaft power 0.69KWH (compressor efficiency 55
%) Actual power 0.72 KWH (Mall - efficiency 95%)
Total actual operating capacity of compressors C1 and C2: 1.89KWH Steam amount on compressor discharge side: C110,3KpC26,2K
P total 16.5 KP The amount of steam on the discharge side is 1.06 times the amount of water vapor in the raw gas.

Power used/steam generated: 114.5 KWH/T
ONThe steam recovered in this way is about 604
, Q KP/lyl 40% at the pressure of tL8A is 1
．． 8 Kg/6d A4i. Each is returned to the equal pressure cylinders of the dryer for reuse.

4. Description of the Drawings FIG. 1 is a flow sheet showing an example of implementing the present invention. FIG. 2 is a flow sheet showing an example in which power consumption can be kept relatively low when there is a large temperature difference between the inlet and outlet of raw gas in FIG.

Claims (1)

[Claims] 1. A mixed gas of a water-insoluble gas and water vapor is brought into direct contact with the circulating water in a condensing heater to heat the circulating water mainly using the latent heat of condensation of the water vapor, thereby lowering the temperature to a lower level. Water-insoluble water vapor that is introduced into an evaporative cooler under pressure, performs self-evaporation adiabatically to lower the water temperature, and is returned to the condensing heater again, and the evaporated water vapor is raised to a predetermined pressure by a compressor. A method of separating and recovering water vapor that mixes with gas. 2. A method for separating and recovering water vapor from a water-insoluble gas as set forth in claim 1, wherein a plurality of sets of circulating water condensing heaters and evaporative coolers are provided.