A six-effect thermal process for extracting nitrate

Abstract

The present invention relates to a process for salt production, specifically a six-effect thermal nitrate extraction process. It comprises the following steps: steam enters the I-effect heating chamber, the II-effect heating chamber, the III-effect heating chamber, the IV-effect heating chamber, the V-effect heating chamber and the VI-effect heating chamber in sequence through a heat pump, and is heated and evaporated in the salt evaporation tank of each effect heating chamber, and the secondary steam temperature after the II-effect evaporation is 105-110°C, and enters the nitrate separation tank for nitrate separation, and a part of the raw steam enters the drying bed for drying; the raw brine is preheated and heated by a plate heat exchanger in sequence and enters the IV, V and VI-effect salt evaporation tanks, and the old brine is preheated and heated by a plate heat exchanger in sequence and enters the I, II and III-effect salt evaporation tanks, and the salt slurry produced by each effect evaporation tank is discharged to a salt collecting box, washed by a three-stage flotation washer, and then centrifuged and dehydrated and dried in a thickener; the present invention can co-produce high-quality salt and Na2SO4, and has high thermal efficiency, which greatly saves production costs.

Description

Technical Field

[0001] The invention relates to a process for producing salt, in particular to a six-effect thermal nitrate extraction process. Background Art

[0002] The majority of domestic well salt brine is Glauber's salt brine, which generally has a high Na2SO4 content. It is not economical to remove it by chemical methods and cannot be considered. At present, there are two main production processes for Glauber's salt brine in China: one is the traditional vacuum salt making, also known as "vacuum evaporation salt making". When multiple evaporation tanks are connected in series to evaporate the liquid (brine), the secondary steam generated by the previous effect is used as the heat source required for the next evaporation process. Vacuum evaporation salt making often uses multi-effect evaporation to improve the utilization rate of thermal energy. At present, four-effect and five-effect evaporation processes account for the vast majority. This method does not extract nitrate, and avoids the enrichment of nitrate by discharging a large amount of old brine. Therefore, the thermal utilization rate is not high, the quality of salt is not high, and the waste of nitrate resources is serious. The second is the salt-nitrate co-production process (also known as mother liquor recovery method) introduced from abroad in the 1990s. This process has high resource utilization, good product quality, and high degree of automation. However, when the Na2SO4 content is high, the output ratio of the salt system with higher thermal utilization rate decreases, and the output ratio of the salt-nitrate separation system with higher energy consumption increases, resulting in a rapid increase in the comprehensive energy consumption of the entire device with the increase of Na2SO4 content. In addition, the process requires brine purification, which further increases the cost. In the market environment where high quality does not mean high price, the competitiveness is low. Therefore, it is necessary to explore energy-saving processes for high-nitrate brine.

[0003] Thermal saltpeter extraction is a saltpeter extraction process developed in China in the early 1980s. It also utilizes the reverse solubility characteristics of Na2SO4 above 17.9°C (the higher the temperature, the lower the solubility), and heats the high-nitrate brine discharged from salt production to about 100°C. Powdered salt is added to the preheated brine or it is evaporated and concentrated in a nitrate evaporator (so it is also called salting-out method). The old brine that is unsaturated with NaCI after heating becomes a saturated solution or a nearly saturated solution. Due to the common ion effect of Na+, Na2SO4 is precipitated to separate salt and saltpeter, and the mother liquor after saltpeter extraction is sent back to the salt production system to produce salt.

[0004] The characteristics of this method are: high thermal efficiency, full recovery of secondary steam, extraction of secondary steam for preheating, improved steam utilization, high salt concentration, small heat loss; short process flow for producing anhydrous sodium sulfate, no brine purification, low investment, closed brine circulation, no discharge of mother liquor, which can reduce the brine consumption of salt production and reduce environmental pollution. The disadvantages are: low quality of salt and poor quality of nitrate. Since the calcium and magnesium impurities in the brine are not removed, some calcium and magnesium impurities enter the nitrate tank. Since the calcium and magnesium impurities enter the sodium sulfate, it is difficult to remove them by washing methods, and it is difficult to improve the quality of nitrate, so that the quality of nitrate can only reach about 95% or even lower, and the commercial value is slightly lower. Therefore, this process has not been promoted. Only Lantian Salt Chemical has persisted for many years, but the benefits are not good. The thermal salt extraction process has low investment, high heat utilization rate, and it is urgent to solve the chronic problem of low product quality. From the analysis of its principle and operation process, the salt washing process requires the old brine Na2SO4 to be as high as possible, even up to 70g / l or more, which will inevitably affect the salt quality, and this contradiction is difficult to resolve. In addition, the process does not use brine purification, and calcium and magnesium impurities have a great impact on product quality. If purification treatment is used, the product quality, especially the quality of anhydrous nitrate, will definitely be greatly improved. However, this will increase investment and operating costs.

[0005] In recent years, with the sharp drop in the price of mirabilite and the sharp rise in fuel prices, the disadvantages of the once popular salt and saltpeter co-production process, which was high in consumption, have gradually emerged, especially in the production of high-nitrate brine, where steam consumption remains high. At a time when the survival of enterprises is at stake, a six-effect thermal salt extraction process is a technical problem that the salt industry urgently needs to solve. Summary of the invention

[0006] The purpose of the present invention is to provide a six-effect thermal nitrate extraction process for the defects of the prior art, which has high thermal efficiency and greatly saves production costs.

[0007] The technical solution of the present invention is implemented as follows: it includes the following steps: the raw steam enters the steam jet heat pump (if the raw steam pressure is not high, the heat pump is not set) to extract part of the I-effect secondary steam to reduce the temperature and pressure and then enter the I-effect heating chamber. The liquid in the I-effect evaporation tank uses the power of the circulating pump to indirectly exchange heat with the steam in the heating chamber and then boils and flashes in the evaporation chamber. The flashed steam enters the II-effect heating chamber through the secondary steam pipe as the heat source of the II-effect. The flash steam of each effect evaporation chamber is used as the heat source of the next effect heating chamber in turn. The II-effect secondary steam is divided into two paths, one path goes to the III-effect heating chamber, and the other path goes to the nitrate heating chamber. The secondary steam of the last effect enters the mixing condenser, and the cooling water sent from the cooling pump room absorbs heat and is condensed into water and discharged into the circulating water pool with the cooling water. The condensed water from each effect is returned to the balance tank of each effect through the condensed water coil. The dry condensed water goes to the condensed water balance tank of effect I for flashing. The condensed water from the previous effects goes to the condensed water tank of the next effect for flashing. The condensed water from effect IV is pumped to the high-temperature plate heat exchanger to preheat the brine. The condensed water from the last effect is pumped to the low-temperature plate heat exchanger to exchange heat with the brine and then discharged to the condensed water pool. A part of the raw steam enters the drying bed for drying; the raw brine is preheated and heated through the plate heat exchanger in turn and then enters the salt evaporation tank of the next few effects; the old brine is preheated and heated through the plate heat exchanger in turn and then enters the nitrate tank; after the secondary steam of the II effect is heated and nitrate is separated, the refined brine is pumped to the salt evaporation tank of the first few effects (the amount of entering the first few effects is determined by the amount of old brine, and the amount of old brine is determined by the content of Na2SO4 in the brine. This description takes the refined brine entering the first three effects as an example); the salt slurry produced by each effect evaporation tank is discharged into the salt collecting box, washed by the three-stage flotation washer, and then sent to the thickener for thickening, centrifugal dehydration and drying; the old brine after washing the salt in the flotation washer goes to the salt settling device, and the clear liquid of the salt settling device is preheated and heated and then enters the nitrate tank for nitrate separation; the salt and nitrate mud at the bottom of the settler are pumped into the nitrate tank, the nitrate slurry in the nitrate tank is centrifugally dehydrated and dried to obtain the finished nitrate, and the clear liquid (refined brine) is transferred to the salt evaporation tank of the first few effects.

[0008] The present invention is realized by the following device, which comprises: an I-effect salt evaporation tank 1, a II-effect salt evaporation tank 2, a III-effect salt evaporation tank 3, a IV-effect salt evaporation tank 4, a V-effect salt evaporation tank 5 and a VI-effect salt evaporation tank 6 connected by pipelines, the raw material inlets of the I-effect salt evaporation tank 1, the II-effect salt evaporation tank 2 and the III-effect salt evaporation tank 3 are connected to the material outlet of a nitrate tank 18 by a pump and a pipeline, the material outlets of the I-effect salt evaporation tank 1, the II-effect salt evaporation tank 2 and the III-effect salt evaporation tank 3 are connected to the inlet of a salt collecting box 8, the raw material inlets of the IV-effect salt evaporation tank 4, the V-effect salt evaporation tank 5 and the VI-effect salt evaporation tank 6 are connected to the low The material outlet of the warm plate heat exchanger 9 is connected through a pipeline, the material outlets of the IV salt evaporation tank 4, the V salt evaporation tank 5 and the VI effect salt evaporation tank 6 are connected to the inlet of the salt collecting box 8, the outlet of the salt collecting box 8 is connected to the inlet of the flotation washer 11 through a salt slurry pump 10 and a pipeline, the bottom outlet of the flotation washer 11 is connected to the inlet of the salt slurry barrel 12, the upper outlet of the flotation washer 11 is connected to the inlet of the salt settling device 13 through a pipeline, the bottom outlet of the salt settling device 13 is connected to the inlet of the salt mud pump 14, the upper outlet of the salt settling device 14 is connected to the inlet of the settler 15, and the upper outlet of the settler 15 is connected to the inlet of the old brine buffer barrel 16.

[0009] The outlet of the old brine buffer barrel 16 is connected to the material inlet of the saltpeter tank 18 through the old brine pump 17 and the pipeline, the outlet of the salt mud pump 14 is connected to the material inlet of the saltpeter tank 18 through the pipeline, the material outlet of the saltpeter tank 18 is connected to the material inlet of the saltpeter thickener 20 through the saltpeter slurry pump 19 and the pipeline, the material outlet of the saltpeter thickener 20 is connected to the inlet of the saltpeter centrifuge 21, and the material outlet of the saltpeter centrifuge 21 is connected to the inlet of the saltpeter drying bed 22; the outlet of the salt slurry barrel 12 is connected to the material inlet of the salt thickener 24 through the salt slurry pump 23 and the pipeline, the material outlet of the salt thickener is connected to the inlet of the salt centrifuge 25, and the outlet of the salt centrifuge 25 is transported to the salt drying bed 27 through the wet salt belt conveyor 26.

[0010] The present invention can co-produce high-quality salt and Na2SO4, has high thermal efficiency, and greatly saves production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a schematic diagram of the process flow of the present invention.

[0012] Figure 2 The device diagram of the present invention is DETAILED DESCRIPTION

[0013] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0014] The present invention comprises the following steps: raw steam enters into a steam jet heat pump to extract part of the I-effect secondary steam, which is then cooled and decompressed and then enters into the I-effect heating chamber; the liquid in the I-effect evaporation tank is indirectly heat-exchanged with the steam in the heating chamber by the power of a circulating pump and then boils and flashes in the evaporation chamber; the flashed steam enters into the II-effect heating chamber through a secondary steam pipe and serves as a heat source for the II-effect. The flashed steam of each effect evaporation chamber serves as a heat source for the next effect heating chamber in turn. The II-effect secondary steam is divided into two paths, one path goes to the III-effect heating chamber and the other path goes to the nitrate heating chamber; the secondary steam of the last effect enters into a mixed condenser, and the cooling water sent from the cooling pump room absorbs heat and is condensed into water and discharged into a circulating water pool along with the cooling water. The condensed water from each effect is returned to the balance tank of each effect through the condensed water coil. The dry condensed water goes to the condensed water balance tank of effect I for flashing. The condensed water from the previous effects goes to the condensed water tank of the next effect for flashing. The condensed water from effect IV is pumped to the high-temperature plate heat exchanger to preheat the brine. The condensed water from the last effect is pumped to the low-temperature plate heat exchanger to exchange heat with the brine and then discharged to the condensed water pool. A part of the raw steam enters the drying bed for drying; the raw brine is preheated and heated through the plate heat exchanger in turn and then enters the salt evaporation tank of the next few effects; the old brine is preheated and heated through the plate heat exchanger in turn and then enters the nitrate tank; after the secondary steam of the II effect is heated and nitrate is separated, the refined brine is pumped to the salt evaporation tank of the first few effects (the amount of entering the first few effects is determined by the amount of old brine, and the amount of old brine is determined by the content of Na2SO4 in the brine. This description takes the refined brine entering the first three effects as an example); the salt slurry produced by each effect evaporation tank is discharged into the salt collecting box, washed by the three-stage flotation washer, and then sent to the thickener for thickening, centrifugal dehydration and drying; the old brine after washing the salt in the flotation washer goes to the salt settling device, and the clear liquid of the salt settling device is preheated and heated and then enters the nitrate tank for nitrate separation; the salt and nitrate mud at the bottom of the settler are pumped into the nitrate tank, the nitrate slurry in the nitrate tank is centrifugally dehydrated and dried to obtain the finished nitrate, and the clear liquid (refined brine) is transferred to the salt evaporation tank of the first few effects.

[0015] The present invention is realized by the following device, which comprises: an I-effect salt evaporation tank 1, a II-effect salt evaporation tank 2, a III-effect salt evaporation tank 3, a IV-effect salt evaporation tank 4, a V-effect salt evaporation tank 5 and a VI-effect salt evaporation tank 6 connected by pipelines, the raw material inlets of the I-effect salt evaporation tank 1, the II-effect salt evaporation tank 2 and the III-effect salt evaporation tank 3 are connected to the material outlet of a nitrate tank 18 by a pump and a pipeline, the material outlets of the I-effect salt evaporation tank 1, the II-effect salt evaporation tank 2 and the III-effect salt evaporation tank 3 are connected to the inlet of a salt collecting box 8, the raw material inlets of the IV-effect salt evaporation tank 4, the V-effect salt evaporation tank 5 and the VI-effect salt evaporation tank 6 are connected to the low The material outlet of the warm plate heat exchanger 9 is connected through a pipeline, the material outlets of the IV salt evaporation tank 4, the V salt evaporation tank 5 and the VI effect salt evaporation tank 6 are connected to the inlet of the salt collecting box 8, the outlet of the salt collecting box 8 is connected to the inlet of the flotation washer 11 through a salt slurry pump 10 and a pipeline, the bottom outlet of the flotation washer 11 is connected to the inlet of the salt slurry barrel 12, the upper outlet of the flotation washer 11 is connected to the inlet of the salt settling device 13 through a pipeline, the bottom outlet of the salt settling device 13 is connected to the inlet of the salt mud pump 14, the upper outlet of the salt settling device 14 is connected to the inlet of the settler 15, and the upper outlet of the settler 15 is connected to the inlet of the old brine buffer barrel 16.

[0016] The outlet of the old brine buffer barrel 16 is connected to the material inlet of the saltpeter tank 18 through the old brine pump 17 and the pipeline, the outlet of the salt mud pump 14 is connected to the material inlet of the saltpeter tank 18 through the pipeline, the material outlet of the saltpeter tank 18 is connected to the material inlet of the saltpeter thickener 20 through the saltpeter slurry pump 19 and the pipeline, the material outlet of the saltpeter thickener 20 is connected to the inlet of the saltpeter centrifuge 21, and the material outlet of the saltpeter centrifuge 21 is connected to the inlet of the saltpeter drying bed 22; the outlet of the salt slurry barrel 12 is connected to the material inlet of the salt thickener 24 through the salt slurry pump 23 and the pipeline, the material outlet of the salt thickener is connected to the inlet of the salt centrifuge 25, and the outlet of the salt centrifuge 25 is transported to the salt drying bed 27 through the wet salt belt conveyor 26.

Claims

1. A six-effect thermal nitrate extraction process, comprising the following steps: The raw steam enters the steam jet heat pump to extract part of the I-effect secondary steam for temperature and pressure reduction, and then enters the I-effect heating chamber. The liquid in the I-effect evaporator uses the power of the circulating pump to indirectly exchange heat with the steam in the heating chamber and then boils and flashes in the evaporation chamber. The flashed steam enters the II-effect heating chamber through the secondary steam pipe and serves as the heat source for the II-effect. The flashed steam in each effect evaporation chamber serves as the heat source for the next effect heating chamber in turn. The secondary steam of effect II is divided into two routes, one route goes to heating chamber of effect III, and the other route goes to heating chamber of nitrate. The secondary steam of the last effect enters the mixed condenser, and the cooling water sent from the cooling pump room absorbs heat and is condensed into water and discharged into the circulating water pool with the cooling water; the condensed water of each effect is returned to the balance barrel of each effect through the condensed water coil, the dry condensed water goes to the condensed water balance barrel of effect I for flashing, the condensed water of the previous effects goes to the condensed water barrel of the next effect for flashing, the condensed water of effect IV is pumped to the high-temperature plate heat exchanger to preheat the brine, and the condensed water of the last effect is pumped to the low-temperature plate heat exchanger to exchange heat with the brine and then discharged To the condensation water pool; a part of the raw steam enters the drying bed for drying; the raw brine is preheated and heated through the plate heat exchanger in turn and then enters the salt evaporation tanks of the latter several effects; the old brine is preheated and heated through the plate heat exchanger in turn and then enters the nitrate tank; after the secondary steam of the II effect is heated and nitrate is separated, the refined brine is pumped to the salt evaporation tanks of the former several effects; the salt slurry produced by each effect evaporation tank is discharged to the salt collecting box, washed by the three-stage flotation washer, and then sent to the thickener for thickening, centrifugal dehydration and drying; the old brine after the salt washing by the flotation washer goes to the salt settling device, the clear liquid of the salt settling device is preheated and heated and then enters the nitrate tank for nitrate separation; the salt and nitrate mud at the bottom of the settler are pumped into the nitrate tank, and the nitrate tank The nitrate slurry is centrifugally dehydrated and dried to obtain finished nitrate, and the refined brine is transferred to the first few salt evaporation tanks; it is achieved by the following device, which includes: an I-effect salt evaporation tank, a II-effect salt evaporation tank, a III-effect salt evaporation tank, an IV-effect salt evaporation tank, a V-effect salt evaporation tank and a VI-effect salt evaporation tank connected by pipelines, the raw material inlets of the I-effect salt evaporation tank, the II-effect salt evaporation tank and the III-effect salt evaporation tank are connected to the material outlet of the nitrate tank through a pump and a pipeline, the material outlets of the I-effect salt evaporation tank, the II-effect salt evaporation tank and the III-effect salt evaporation tank are connected to the inlet of the salt collecting box, the IV salt evaporation tank, the V salt evaporation tank The raw material inlet of the VI effect salt evaporation tank is connected to the material outlet of the low-temperature plate heat exchanger through a pipeline, the material outlets of the IV salt evaporation tank, the V salt evaporation tank and the VI effect salt evaporation tank are connected to the inlet of the salt collecting box, the outlet of the salt collecting box is connected to the inlet of the flotation washer through a salt slurry pump and a pipeline, the bottom outlet of the flotation washer is connected to the inlet of the salt slurry barrel, the upper outlet of the flotation washer is connected to the inlet of the salt settling device through a pipeline, the bottom outlet of the salt settling device is connected to the inlet of the salt slurry pump, the upper outlet of the salt settling device is connected to the inlet of the settler, and the upper outlet of the settler is connected to the inlet of the old brine buffer barrel; The method is realized by the following device, which comprises: an effect I salt evaporator, an effect II salt evaporator, an effect III salt evaporator, an effect IV salt evaporator, an effect V salt evaporator and an effect VI salt evaporator connected by pipelines, the raw material inlets of the effect I salt evaporator, the effect II salt evaporator and the effect III salt evaporator are connected with the material outlet of the first plate heat exchanger by pipelines, the material outlets of the effect I salt evaporator, the effect II salt evaporator and the effect III salt evaporator are connected with the inlet of a salt collecting box, the material outlets of the effect IV salt evaporator, the effect V salt evaporator and the effect VI salt evaporator are connected with the inlet of a salt collecting box ... I salt evaporator, the effect II salt evaporator and the effect V salt evaporator are connected with the inlet of a salt collecting box, the material outlets of the effect The raw material inlet is connected to the material outlet of the second plate heat exchanger through a pipeline, the material outlets of the IV salt evaporation tank, the V salt evaporation tank and the VI effect salt evaporation tank are connected to the inlet of the salt collecting box, the outlet of the salt collecting box is connected to the inlet of the flotation washer through a salt slurry pump and a pipeline, the bottom outlet of the flotation washer is connected to the inlet of the salt slurry barrel, the upper outlet of the flotation washer is connected to the inlet of the salt settling device through a pipeline, the bottom outlet of the salt settling device is connected to the inlet of the salt mud pump, the upper outlet of the salt settling device is connected to the inlet of the settler, and the upper outlet of the settler is connected to the inlet of the old brine buffer barrel.

2. A six-effect thermal nitrate extraction process as claimed in claim 1, characterized in that: The outlet of the brine buffer barrel is connected to the material inlet of the nitrate tank through an old brine pump and a pipeline, the outlet of the saltpeter pump is connected to the material inlet of the nitrate making tank through a pipeline, the material outlet of the nitrate tank is connected to the material inlet of the nitrate thickener through a nitrate slurry pump and a pipeline, the material outlet of the nitrate thickener is connected to the inlet of the nitrate centrifuge, and the material outlet of the nitrate centrifuge is connected to the inlet of the nitrate drying bed.

3. A six-effect thermal nitrate extraction process as claimed in claim 1, characterized in that: The outlet of the salt slurry barrel is connected to the material inlet of the salt thickener through a salt slurry pump and a pipeline, the material outlet of the salt thickener is connected to the inlet of the salt centrifuge, and the outlet of the salt centrifuge is transported to the salt drying bed through a wet salt belt conveyor.

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