Evaporation energy-saving process for liquid caustic soda concentration

Abstract

The invention discloses an evaporation energy-saving process for liquid caustic soda concentration, which comprises the following steps: S1, preheating: S11, preparing a liquid caustic soda solution with a certain concentration, and then feeding the liquid caustic soda solution through a feeding pump; s12, then the alkali solution is preheated; and S2, primary evaporation and concentration, which comprises the following sub-steps: S21, continuously feeding the preheated material into a primary heater, heating liquid caustic soda in the primary heater to an overheated state, and feeding the heated liquid caustic soda into a primary separation chamber for vapor-liquid separation. According to the evaporation energy-saving process for liquid caustic soda concentration, secondary steam is subjected to staged compression, the performance of an existing steam compressor is combined, steam temperature rise is reasonably controlled, the influence of boiling point rise on system operation is reduced, system energy consumption is reduced to the maximum extent, a pipeline system between equipment is simple, operation and operation are simple and stable, automatic control is easy to achieve, and the energy-saving effect is good. The occupied area is small, and evaporation is relatively mild.

Description

Technical Field

[0001] The invention relates to the technical field of evaporation energy saving for liquid alkali concentration, in particular to an evaporation energy saving process for liquid alkali concentration. Background Art

[0002] Liquid caustic soda concentration is an important step in the preparation of caustic soda. At present, the method of evaporating the water in the liquid caustic soda by a heater is usually used to concentrate the liquid caustic soda. Since the steam price is high in most parts of the country and the electricity price is relatively low, MVR evaporation technology has attracted much attention. However, for high-boiling point solutions such as liquid caustic soda, while maintaining the effective heat transfer temperature difference of the system, the steam compressor is required to increase the temperature of the secondary steam to a relatively high level, which places relatively high performance requirements and energy consumption on the steam compressor. Moreover, currently there are only double-effect or triple-effect evaporation concentrations for liquid caustic soda concentration, but due to the large amount of steam consumption, the operating costs are relatively high.

[0003] Therefore, we proposed an evaporation energy-saving process for liquid alkali concentration in order to solve the problems raised above. Summary of the invention

[0004] The object of the present invention is to provide an energy-saving evaporation process for liquid alkali concentration, so as to solve the problem raised in the above-mentioned background technology that for high-boiling point solutions such as liquid alkali in the current market, while maintaining the effective heat transfer temperature difference of the system, the steam compressor is required to increase the temperature of the secondary steam to a relatively high level, which places relatively high performance requirements and energy consumption on the steam compressor. Moreover, currently there is only double-effect or triple-effect evaporation concentration for liquid alkali concentration, but due to the large amount of steam consumption, the operating cost is relatively high.

[0005] To achieve the above object, the present invention provides the following technical solution: an evaporation energy-saving process for liquid alkali concentration, comprising the following steps:

[0006] S1, preheating, including the following sub-steps:

[0007] S11, first prepare a liquid alkali solution of a certain concentration, and then feed the liquid alkali solution through a feed pump;

[0008] S12, then preheating the alkaline solution, the preheating is divided into startup preheating and normal production preheating;

[0009] S2, primary evaporation and concentration, comprising the following sub-steps:

[0010] S21, the preheated material continuously enters the primary heater, and the liquid alkali is heated to a superheated state in the primary heater and then enters the primary separation chamber for vapor-liquid separation;

[0011] S22, using a vacuum pump to establish a vacuum, the non-condensable gas generated during the evaporation process is condensed and cooled by a non-condensable gas condenser, and then continuously sucked in and discharged by the vacuum pump;

[0012] S23, transfer to the secondary evaporation concentration through the transfer pump, and the separated secondary steam enters the primary compression;

[0013] S3, secondary evaporation and concentration, comprising the following sub-steps:

[0014] S31, the concentrated liquid from the transfer pump of the primary separation chamber enters the secondary heater, is heated to a superheated state in the secondary heater, and then enters the secondary separation chamber for vapor-liquid separation;

[0015] S32, vacuum is also established by using a vacuum pump, and the non-condensable gas generated during the evaporation process is condensed and cooled by a non-condensable gas condenser, and then continuously sucked in and discharged by the vacuum pump;

[0016] S33, after the alkali concentration of the concentrated liquid reaches 50% through the secondary evaporation, it is transferred to the preheater A through the discharge pump, and the separated secondary steam also enters the primary compression;

[0017] S4, cooling of finished liquid caustic soda, comprising the following sub-steps:

[0018] S41, after the concentrated caustic soda liquid temperature coming out of the preheater A is reduced to 80-85°C, it is cooled to 45°C in a cooler to obtain 50% finished caustic soda liquid;

[0019] S5, steam primary compression, including the following sub-steps:

[0020] S51, the secondary steam coming out of the primary separation chamber and the secondary separation chamber merges and enters the primary compression, and the temperature of the secondary steam is increased from 70°C to 105°C by the compressor;

[0021] S52, part of the heated secondary steam is used to provide heat to the first-stage heater, and part enters the second-stage compression;

[0022] S6, steam secondary compression, comprising the following sub-steps:

[0023] S61, part of the secondary steam compressed from the first stage, the temperature of the secondary steam is increased from 105°C to 123°C through the compressor, and is used to provide heat for the secondary heater;

[0024] S7, condensate discharge, including the following sub-steps:

[0025] S71. After heat exchange, the secondary steam is liquefied into steam condensate, which is preheated and heated by the preheater B to feed liquid alkali, and finally enters the condensate collection and treatment system.

[0026] Preferably, the concentration of the liquid alkali solution in S11 is 32%, and the initial temperature range is 70-80°C.

[0027] Preferably, the startup preheating adopts a method of introducing 0.4-0.6MPaG saturated raw steam for heating to initially preheat the liquid alkali solution in the evaporation system;

[0028] The specific preheating steps are as follows: After the feeding process is completed, open the compressor inlet and outlet pipeline balancing valves, the compressor starts to run at a low speed, and at the same time open the raw steam regulating valve. When the liquid temperature reaches the evaporation temperature, the compressor starts to increase speed, and the system automatically closes the raw steam valve, stops using raw steam, switches to the evaporation process, and the preheating ends.

[0029] Preferably, the specific preheating steps of the normal production preheating are as follows: the material is pumped in by a feed pump, passes through preheater A and preheater B respectively, exchanges heat with the concentrated liquid alkali and condensed water, the temperature rises to 95-100°C, and then enters the first-level evaporation concentration, and a small amount of raw steam is added according to the heating situation to keep the evaporation stable.

[0030] Preferably, the evaporation temperature in S21 is 88-97° C., the evaporation pressure is 0.03 MPaA, and the concentration of the liquid alkali after primary evaporation and concentration reaches 38-40%.

[0031] Preferably, the evaporation temperature in S31 is 97-115° C., and the evaporation pressure is 0.03 MPaA.

[0032] Preferably, in S51, since the temperature rise of the first-stage compression of the steam is relatively high, a two-stage compressor is used or two compressors are connected in series to compress the secondary steam twice, thereby achieving the required temperature rise of 35°C.

[0033] Preferably, in S51, the secondary steam is compressed by the compressor impeller to increase the pressure and temperature of the secondary steam, and after the enthalpy value is increased, it is used as a heat source.

[0034] Preferably, in S61, since the temperature rise of the steam in the second-stage compression is only 18° C., the required temperature can be reached by using a single compressor.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows: the energy-saving evaporation process for liquid alkali concentration, by performing graded compression on the secondary steam, combined with the performance of the existing steam compressor, reasonably controls the steam temperature rise, reduces the influence of the boiling point rise on the system operation, and reduces the system energy consumption to the maximum extent, making the MVR evaporation technology feasible in the liquid alkali concentration industry. The main energy consumption is the electric energy of the compressor, the operating cost is lower than that of the three-effect evaporation, the structure is simple, the equipment is less, and the pipeline system between the equipment is simple compared to the three-effect evaporation, the operation is simple and stable, it is easy to realize automatic control, the floor space is small, and the evaporation is relatively mild. The specific contents are as follows:

[0036] (1) By using the secondary steam generated by each stage of heaters when evaporating liquid caustic soda as the evaporation heat source of the next stage of heaters, the purpose of reducing the consumption of raw steam in the entire system is achieved, so that the raw steam consumption per ton of caustic soda is about 0.5 tons;

[0037] (2) Utilizing the latent heat of secondary steam during the evaporation process, the steam compressor compresses the volume of secondary steam to convert it into high-temperature and high-pressure steam. In this process, the steam compressor consumes electrical energy to increase the energy grade of secondary steam so that it can be reused as a heat source, thereby realizing the recycling of energy and achieving the purpose of reducing process energy consumption;

[0038] (3) The concentration of liquid alkali is divided into two stages, primary evaporation concentration and secondary evaporation concentration. The secondary steam is compressed once and then separated into two streams, one of which directly supplies heat to the primary evaporation concentration, and the other steam is compressed again and then supplies heat to the secondary evaporation concentration, thereby realizing the graded compression of the secondary steam, reasonably controlling the steam temperature rise, and minimizing the energy consumption of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 The figure is a flow chart of the evaporation energy-saving process of the present invention. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] See also Figure 1 , the present invention provides the following technical solutions:

[0042] Embodiment 1: The evaporation energy-saving process for liquid caustic soda concentration in this embodiment comprises the following steps:

[0043] Step 1: Preheating, including the following sub-steps:

[0044] 1. First prepare a liquid caustic soda solution with a concentration of 32% and an initial temperature range of 70-80°C, and then feed the liquid caustic soda solution through a feed pump;

[0045] 2. Then preheat the alkali solution. When starting up for the first time, use the startup preheating method. The startup preheating adopts the method of introducing 0.4-0.6MPaG saturated raw steam for heating, and the liquid alkali solution in the evaporation system is initially preheated. The specific preheating steps are as follows: After the feeding process is completed, open the compressor inlet and outlet pipeline balance valve, the compressor starts to run at a low speed, and the raw steam regulating valve is opened at the same time. When the feed liquid temperature reaches the evaporation temperature, the compressor starts to increase the speed. After generating secondary steam, the system operates normally, and steam condensate and concentrated materials are generated. The system automatically closes the raw steam valve, stops using raw steam, and uses the waste heat of condensate and materials for preheating. After that, there is no need to start the machine for preheating, switch to the evaporation process, and the preheating is completed;

[0046] Normal production preheating is used in other stages. The specific preheating steps of normal production preheating are as follows: the material is pumped in by the feed pump, passes through preheater A and preheater B respectively, exchanges heat with the concentrated liquid alkali and condensed water, and the temperature rises to 95-100℃, and then enters the first-level evaporation concentration. A small amount of raw steam is added according to the heating situation to keep the evaporation stable;

[0047] Step 2: primary evaporation and concentration, including the following sub-steps:

[0048] 1. The preheated materials continuously enter the first-stage heater. After the liquid alkali is heated to a superheated state in the first-stage heater, it enters the first-stage separation chamber for vapor-liquid separation. The evaporation temperature is 88-97°C, and the evaporation pressure is 0.03MPaA. The concentration of the liquid alkali after first-stage evaporation concentration reaches 38-40%;

[0049] 2. Use a vacuum pump to create a vacuum. The non-condensable gas generated during the evaporation process is condensed and cooled by the non-condensable gas condenser, and then continuously sucked in and discharged by the vacuum pump;

[0050] 3. The material is transferred to the secondary evaporation and concentration through the transfer pump, and the separated secondary steam enters the primary compression;

[0051] Step 3: Secondary evaporation and concentration, including the following sub-steps:

[0052] 1. The concentrated liquid from the transfer pump of the first-stage separation chamber enters the second-stage heater, and after being heated to a superheated state in the second-stage heater, enters the second-stage separation chamber for vapor-liquid separation. The evaporation temperature is 97-115°C, and the evaporation pressure is 0.03MPaA;

[0053] 2. The vacuum is also established by using a vacuum pump. The non-condensable gas generated during the evaporation process is condensed and cooled by the non-condensable gas condenser, and then continuously sucked in and discharged by the vacuum pump;

[0054] 3. After the alkali concentration of the concentrated liquid reaches 50% through the secondary evaporation, it is transferred to the preheater A through the discharge pump, and the separated secondary steam also enters the primary compression;

[0055] Step 4: Cooling the finished liquid caustic soda, including the following sub-steps:

[0056] 1. After the concentrated caustic soda temperature from preheater A is reduced to 80-85°C, it is cooled to 45°C in a cooler to obtain 50% finished caustic soda;

[0057] Step 5: primary steam compression, including the following sub-steps:

[0058] 1. The secondary steam coming out of the primary separation chamber and the secondary separation chamber merge and enter the primary compression. The temperature of the secondary steam is raised from 70°C to 105°C by the compressor. During the evaporation of liquid alkali, since the temperature of the steam is lower than the temperature of the solution, the effective temperature difference of the heat transfer process cannot be maintained by the secondary steam itself, and a compressor is required to increase the temperature of the secondary steam. The present invention adopts mechanical steam recompression technology to compress the secondary steam through the compressor impeller to increase the pressure and temperature of the secondary steam. After the enthalpy value increases, it is used as a heat source. Since the temperature rise of the primary compression of steam is relatively high, a two-stage compressor or two compressors in series are required to compress the secondary steam twice, thereby achieving the required temperature rise of 35°C.

[0059] 2. Part of the heated secondary steam is used to provide heat to the first stage heater, and part enters the second stage compression;

[0060] Step 6: Secondary compression of steam, including the following sub-steps:

[0061] 1. The temperature of part of the secondary steam compressed from the first stage is raised from 105°C to 123°C by the compressor to provide heat for the secondary heater. Since the temperature rise of the steam in the second stage compression is only 18°C, a single compressor can reach the required temperature;

[0062] Step 7: Condensate discharge, including the following sub-steps:

[0063] 1. After heat exchange, the secondary steam is liquefied into steam condensate, which is preheated by preheater B to raise the temperature of the feed liquid alkali, and finally enters the condensate collection and treatment system.

[0064] According to market conditions, the current raw steam consumption per ton of alkali in triple-effect evaporation is 0.5 tons, the electricity consumption is 5 kWh, and the circulating water consumption is 38.4 tons. The graded MVR evaporation per ton of alkali consumes a small amount of raw steam for preheating and compressor sealing, about 0.029 tons, with an electricity consumption of 121.11 kWh and a circulating water consumption of 0.013 tons. Based on the raw steam unit price of 180 yuan / ton, the electricity price of 0.6 yuan / kWh and the circulating water unit price of 0.2 yuan / ton, the operating cost of triple-effect evaporation per ton of alkali is 99.96 yuan, and the operating cost of graded MVR per ton of alkali is 77.85 yuan, saving 22.11 yuan and reducing the annual operating cost by 2.21 million yuan, which is of considerable value.

[0065] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An evaporation energy-saving process for liquid caustic soda concentration, characterized in that: The following steps are involved: S1, preheating, including the following sub-steps: S11, first prepare a liquid alkali solution of a certain concentration, and then feed the liquid alkali solution through a feed pump; S12, then preheating the alkaline solution, the preheating is divided into startup preheating and normal production preheating; S2, primary evaporation and concentration, comprising the following sub-steps: S21, the preheated material continuously enters the primary heater, and the liquid alkali is heated to a superheated state in the primary heater and then enters the primary separation chamber for vapor-liquid separation; S22, using a vacuum pump to establish a vacuum, the non-condensable gas generated during the evaporation process is condensed and cooled by a non-condensable gas condenser, and then continuously sucked in and discharged by the vacuum pump; S23, transfer to the secondary evaporation concentration through the transfer pump, and the separated secondary steam enters the primary compression; S3, secondary evaporation and concentration, comprising the following sub-steps: S31, the concentrated liquid from the transfer pump of the primary separation chamber enters the secondary heater, is heated to a superheated state in the secondary heater, and then enters the secondary separation chamber for vapor-liquid separation; S32, vacuum is also established by using a vacuum pump, and the non-condensable gas generated during the evaporation process is condensed and cooled by a non-condensable gas condenser, and then continuously sucked in and discharged by the vacuum pump; S33, after the alkali concentration of the concentrated liquid reaches 50% through the secondary evaporation, it is transferred to the preheater A through the discharge pump, and the separated secondary steam also enters the primary compression; S4, cooling of finished liquid caustic soda, comprising the following sub-steps: S41, after the concentrated caustic soda liquid temperature coming out of the preheater A is reduced to 80-85°C, it is cooled to 45°C in a cooler to obtain 50% finished caustic soda liquid; S5, steam primary compression, including the following sub-steps: S51, the secondary steam coming out of the primary separation chamber and the secondary separation chamber merges and enters the primary compression, and the temperature of the secondary steam is increased from 70°C to 105°C by the compressor; S52, part of the heated secondary steam is used to provide heat to the first-stage heater, and part enters the second-stage compression; S6, steam secondary compression, comprising the following sub-steps: S61, part of the secondary steam compressed from the first stage, the temperature of the secondary steam is increased from 105°C to 123°C through the compressor, and is used to provide heat for the secondary heater; S7, condensate discharge, including the following sub-steps: S71. After heat exchange, the secondary steam is liquefied into steam condensate, which is preheated and heated by the preheater B to feed liquid alkali, and finally enters the condensate collection and treatment system.

2. The evaporation energy-saving process for liquid caustic soda concentration according to claim 1 is characterized in that: The concentration of the liquid alkali solution in S11 is 32%, and the initial temperature range is 70-80°C.

3. The evaporation energy-saving process for liquid caustic soda concentration according to claim 1 is characterized in that: The startup preheating adopts the method of introducing 0.4-0.6MPaG saturated raw steam for heating, and initially preheats the liquid alkali solution in the evaporation system; The specific preheating steps are as follows: After the feeding process is completed, open the compressor inlet and outlet pipeline balancing valves, the compressor starts to run at a low speed, and at the same time open the raw steam regulating valve. When the liquid temperature reaches the evaporation temperature, the compressor starts to increase speed, and the system automatically closes the raw steam valve, stops using raw steam, switches to the evaporation process, and the preheating ends.

4. The evaporation energy-saving process for liquid caustic soda concentration according to claim 1 is characterized in that: The specific preheating steps of the normal production preheating are as follows: the material is pumped in by the feed pump, passes through preheater A and preheater B respectively, exchanges heat with the concentrated liquid alkali and condensed water, the temperature rises to 95-100°C, and then enters the first-level evaporation concentration, and a small amount of raw steam is added according to the heating situation to keep the evaporation stable.

5. The evaporation energy-saving process for liquid caustic soda concentration according to claim 1 is characterized in that: The evaporation temperature in S21 is 88-97° C., the evaporation pressure is 0.03 MPaA, and the concentration of the liquid alkali after the first-stage evaporation concentration reaches 38-40%.

6. The evaporation energy-saving process for liquid caustic soda concentration according to claim 1 is characterized in that: The evaporation temperature in S31 is 97-115° C., and the evaporation pressure is 0.03 MPaA.

7. The evaporation energy-saving process for liquid caustic soda concentration according to claim 1 is characterized in that: In S51, since the temperature rise of the first-stage steam compression is relatively high, a two-stage compressor or two compressors connected in series are required to compress the secondary steam twice to achieve the required temperature rise of 35°C.

8. The evaporation energy-saving process for liquid caustic soda concentration according to claim 1 is characterized in that: In S51, the secondary steam is compressed by the compressor impeller to increase the pressure and temperature of the secondary steam. After the enthalpy value is increased, the secondary steam is used as a heat source.

9. The evaporation energy-saving process for liquid caustic soda concentration according to claim 1, characterized in that: In S61, since the temperature rise of the steam in the second-stage compression is only 18° C., the required temperature can be reached by using a single compressor.

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