6.NaCl-Na2S04-H20体系热循环法盐硝联产工艺.doc

NaCl-Na2SO4-H2O体系热循环法盐硝联产工艺彭赛军（中国中轻国际工程有限公司 北京100026）内容摘要本文就NaCl-Na2SO4-H2O卤水现有热法盐硝联产工艺进行分析，结合兑卤循环法工艺，提出热循环法盐硝联产工艺供同行参考。关键词：热循环法 盐硝联产一.现有热法盐硝联产工艺分析有关岩盐盐矿硫酸钠型卤水组分范围见表1。 表1 硫酸钠型卤水组分企业名称单位NaClNa2SO4CaSO4MgSO4H2O中盐镇江盐矿g/l29013.863.640.33江苏华尔润公司g/l30022.02.500.80安徽长江盐矿g/l28616.172.200.27广东龙归盐矿g/l28015.00.690.13湖南湘澧盐矿g/l30032.01.281.53江西盐矿g/l30025.01.600.80湖北728盐矿g/l28817.32.510.65硫酸钠型卤水忽略少量杂质条件下为NaCl-Na2SO4-H2O体系。在高于常温的条件下，该体系呈NaCl的溶解度随温度的升高而增加、Na2SO4的溶解度随温度的升高而降低的趋势，有关相图数据见表2。表2 NaCl-Na2SO4-H2O体系有关相图数据温度单位NaClNa2SO4H2O备注150g/l34959808NaCl+Na2SO4105g/l31653841NaCl+Na2SO4100g/l30754849NaCl+Na2SO490g/l30854847NaCl+Na2SO475g/l30257850NaCl+Na2SO460g/l29863849NaCl+Na2SO455g/l29662852NaCl+Na2SO450g/l29365853NaCl+Na2SO445g/l28470857NaCl+Na2SO4作者简介：彭赛军（1958-）男 中国中轻国际工程有限公司副总工程师 主要从事盐化工研究设计工作。根据上述盐硝溶解规律，现有主要热法盐硝联产生产工艺有：1.盐析法盐硝联产工艺热盐析法盐硝联产工艺流程见图1。 真空系统 蒸汽 效制盐 效制盐 效制盐 效制盐 盐析母液 硫酸钠 盐析 预热 预热 预热 洗盐 氯化钠 洗盐母液 氯化钠 原卤图1 热盐析法盐硝联产工艺流程图 该工艺以盐析母液顺流进料、顺流排盐，末效蒸发罐集中排出盐浆经过常温原卤降温回溶其中硫酸钠，洗后盐经过脱水干燥为成品盐；洗盐母液经过冷凝水和二次蒸汽预热至90加入氯化钠盐析，盐析硝洗涤、脱水和干燥后为成品硝。有关生产实际数据见表3。表3 湖北云应地区热盐析法盐硝联产生产数据名称单位温度NaClNa2SO4CaSO4MgSO4H2O原卤g/l25270.526.461.521.05一次洗卤沉淀物%3026.948.701.900.0662.4洗盐卤水g/l30285.2578.060.661.18效料液g/l140311.054.520.330.29效料液g/l125305.054.860.410.36效料液g/l100306.756.580.211.09效料液g/l60304.256.360.215.45盐析母液g/l90306.756.580.211.18盐析硝%909.8250.4431.360.467.92精制盐%7095.090.370.020.014.36根据生产实际情况分析，该工艺需要解决的主要问题有：1）兑卤降温洗盐富集硫酸钠受到温度和溶解度的局限。根据表2分析：常温下卤水中硫酸钠饱和溶解度为80.8 g/l，90温度下卤水中硫酸钠饱和溶解度为52.0 g/l，理论上当原卤含硝量超过30 g/l，通过原卤洗涤盐硝浆料回溶硫酸钠受到限制。2）洗盐卤水预热盐析结垢。根据表3分析：洗盐卤水预热盐析过程是氯化钠溶解、硫酸钠和硫酸钙析出过程，二次蒸汽预热器的使用受到结垢、频繁冲洗的影响。3）卤水中钙镁杂质析出。根据表3分析：原卤在洗盐过程中硫酸钙析出；洗盐卤水预热盐析过程硫酸钙、硫酸镁析出，制盐蒸发过程硫酸钙析出，影响产品氯化钠、硫酸钠的质量。4）采用四效蒸发制盐工艺，影响制盐蒸发热经济。根据现有工艺和自动控制技术的进步，采用以下措施该工艺有关技术经济指标可以得到改善提高。1）采用卤水净化工艺除去原卤中的钙镁杂质，可以提高产品硫酸钠的质量达到99%以上；2）采用五效蒸发替代四效蒸发制盐工艺，可使制盐蒸发系统热经济达到3.79以上；3）采用DCS自控系统，可连续稳定的控制生产系统，年有效生产时间可达到320天以上；4）采用精卤洗盐和末效制盐母液循环的方式，可以提高产品精制盐质量达到99.1%以上；5）采用洗盐母液蒸发析硝替代盐析析硝方式，有利于过程控制产品硫酸钠的质量。2.引进蒸发法盐硝联产工艺 引进蒸发法盐硝联产工艺流程见图2。 预热 预热 预热 精卤 真空系统 蒸汽 201制盐 202制盐 203制盐 304制盐 氯化钠蒸汽 301制硝 302闪蒸 制盐母液析硝母液硫酸钠 预热 预热 图2 引进蒸发法盐硝联产工艺流程图该工艺以精卤经过冷凝水、二次蒸汽预热后顺流进料，201至304蒸发制盐、平流以精卤盐腿淘洗后排盐、洗后盐经过脱水和干燥为成品盐；制盐母液经闪蒸罐302和制硝罐301二次蒸汽预热后进入301热泵制硝蒸发罐蒸发，硝浆以304制盐母液淘洗、脱水和干燥后为产品硝。有关生产实际数据见表4。表4 硫酸钠型卤水引进蒸发法盐硝联产生产数据名称单位温度运行数据共饱溶液备注NaClNa2SO4NaClNa2SO4精卤g/l30300.015.0277.080.8201料液g/l107339.021.07306.054.3202料液g/l85.6329.029.85305.053.7203料液g/l63.3310.047.16299.058.2304料液g/l47.9296.062.29294.064.0301料液g/l98309.053.74307.053.7302料液g/l78.2305.053.97304.055.2硫酸钠%700.8099.0精制盐%7099.50.20根据生产实际情况分析：采用热泵四效蒸发制盐，由于热泵压缩比的限制，单位面积传热蒸发能力较低、加热面积较大；制硝母液闪蒸罐302和制盐母液预热器305和306结垢。根据现有工艺和自动控制技术的进步，采用以下措施该工艺有关技术经济指标可以改善提高。1）采用硝水循环方式淘洗硝浆，可以提高硝质量达到99.5%以上；2）采用五效蒸发替代热泵四效蒸发制盐工艺，可以提高制盐蒸发热经济达到3.79以上；3）取消热泵蒸发制盐可以提高制盐单位面积蒸发能力；同时改善工艺对原料卤水中含硝量变化的适应范围；4）取消闪蒸罐，避免提硝系统因结垢而造成生产稳定性下降，延长有效生产时间；5）采用强制带固体循环换热器（申请专利设备）运行，可以改善预热器305和306结垢情况。二.推荐工艺流程综合上述两种热法盐硝联产工艺分析，其应用于硫酸钠型卤水尚存在可以改进之处。本文结合过去提出的兑卤循环法盐硝联产工艺，提出循环法盐硝（或硝盐）联产新工艺路线（申请专利号200610114043.8）。工艺流程见图3。 预热 预热 预热 蒸发脱氧 精卤真空系统 蒸汽 201制盐 202制盐 203制盐 204制盐 205制盐氯化钠 预热 预热制盐母液蒸汽 301制硝 析硝母液硫酸钠 图3 循环法盐硝联产工艺流程图精卤经过冷凝水换热后进入蒸发脱氧器蒸发浓缩，脱氧精卤经过至效二次蒸汽预热，顺流进制盐至效，盐浆平流精卤淘洗排至盐脱水、干燥工序。效排出制盐母液经过效制盐蒸发罐和热泵制硝蒸发罐二次蒸汽预热、热泵制硝罐蒸发制硝，硝浆经过循环硝水淘洗排至硝脱水、干燥工序，制硝母液循环至制盐蒸发系统蒸发制盐。根据原卤成分：NaCl 286g/l Na2SO4 16g/l CaSO4 1.0g/l MgSO4 0.6g/l。年产60万吨精制盐、3万吨/年硫酸钠规模装置，循环法盐硝联产新工艺各工序主要操作参数和设备选型：1.五效蒸发制盐：效生蒸汽压力3kgf/cm2（表压）、温度143；效真空度0.092MPa、料液温度48。各效罐内盐浆固液比15-30%，精卤排盐固液比50%。精卤流量280m3/h，制盐母液循环量448m3/h，小时产盐量78t/h。采用强制循环轴向进料蒸发罐。2.精卤浓缩脱氧：混合冷凝水预热精卤至48，精卤流量280m3/h，经过效制盐蒸发罐二次蒸汽加热和蒸发、浓缩脱氧器真空度0.092MPa，料液温度48。采用强制循环轴向进料浓缩脱氧器。3.精卤二次蒸汽预热：浓缩脱氧后精卤采用至效二次蒸汽预热，精卤初始温度48、终温115。浓缩精卤274m3/h。采用列管式换热器。4.真空系统：制盐效真空系统采用喷雾冷凝塔、二级蒸汽喷射和一级水喷射组成，真空度0.092MPa，循环冷却水上水温度32、下水温度38。5.制盐母液预热：效二次蒸汽预热制盐母液进口温度48、出口温度56；制硝和效二次蒸汽预热制盐母液进口温度56、出口温度75。制盐母液流量448m3/h。6.热泵蒸发制硝：工作蒸汽压力3kgf/cm2（表压）、温度151，料液温度90，制硝母液组分：NaCl 308g/l Na2SO4 54g/l。制硝母液流量429m3/h。循环硝水淘洗硝浆固液比50%。采用强制循环轴向进料蒸发罐。7.产品质量：精制盐含NaCl 99.5%以上；无水硝含Na2SO4 99.5%以上。蒸发工序操作参数见表5；主要设备见表6。表5 有关蒸发工序工艺参数项目效效效效效制硝加热室蒸汽温度1401181008263100加热室压力MPa（绝压）0.340.190.100.050.020.10蒸发室液温13011090694890蒸发室压力MPa（绝压）0.190.100.050.020.010.05料液Na2SO4成分（g/l）19.224.633.255.062.054.0共饱和卤水Na2SO4成分（g/l）54.854.551.656.564.051.6卤水进料量m3/h274234182135+42992+411448卤水出料量m3/h23418213592+411448429表6 蒸发预热工序主要设备表序号名称规格数量备注1制盐蒸发罐F=1000m252浓缩脱氧器F=200m213精卤预热器F=300m254制盐母液预热器F=1000m225制硝蒸发罐F=1000m21三.初步工艺和热量计算（一）计算原始数据 1.生产规模：年产60万吨精制盐、3万吨无水硝。 2.年有效生产时间：7680小时。 3. 卤水成分：精卤、制盐母液和制硝母液成分见表7。表7 卤水成分表序号名称温度单位成分NaClNa2SO41精 卤30g/l286162制盐母液48g/l295623制硝母液90g/l30854（二）物料衡算1.每小时产盐量=年产盐量年有效生产时间=6000007680=78t/h2.每小时需卤量=每小时产盐量卤水含盐量氯化钠收率=780.2860.975=280m3/h3.每小时产硝量=每小时需卤量卤水含硝量硫酸钠收率=2800.0160.9=4t/h（三）热量衡算 1.制硝母液效二次蒸汽闪蒸量=制硝母液流量比重比热温降汽化热 =429m3/h1200kg/m30.78kcal/kg.21557kcal/kg=15.14 t/h2.制盐母液预热效二次蒸汽用量=制盐母液流量比重比热温升汽化热 =448 m3/h1200 kg/m30.78 kcal/kg.12557 kcal/kg =9.03 t/h3.浓缩脱氧蒸发量=（制硝母液效闪蒸量-制盐母液预热效二次蒸汽用量）蒸发比值 =（15.14 t/h -9.03t/h）0.909=5.55t/h4.制硝蒸发水量=制盐母液循环量-制硝母液量-理论产硝量=448m3/h -429m3/h -280m3/h16kg/m32600kg/m3=17.28t/h5.总蒸发水量=每小时产盐量卤水含盐量（卤水比重-卤水含盐量-卤水含硝量）=78t/h0.286t/m3（1200kg/m3-286kg/m3-16kg/m3）=244.91t/h6.制盐蒸发水量=总蒸发水量-（1+3+4）蒸发量=244.91t/h-（15.14+5.55+17.28）=206.94t/h7.制盐蒸发耗汽量=制盐蒸发水量热经济=206.943.79=54.60t/h8.制硝蒸发耗汽量=（制硝蒸发水量引射比）混合比=（17.281/3）165=18.43t/h9.吨产品蒸发耗汽量=（制盐耗汽量+制硝耗汽量）盐硝产量 =（54.60+18.43）（78+4）=0.89吨汽/吨产品10.蒸发系统热经济=总蒸发水量总蒸汽消耗量=244.91（54.60+18.43）=3.35四.初步分析结论 1.本工艺制盐采用五效等面积蒸发，有利于实现100万吨/年级规模装置标准和非标准设备国产化、大型化。 2.取消闪蒸罐，制盐母液采用强制循环预热器，有利于简化工艺流程，改善提硝系统结垢状况，可延长有效生产周期。 3.本工艺利用制硝母液效闪蒸二次蒸汽进行精卤蒸发浓缩脱氧，有利于提高系统的热经济，减少蒸发系统设备腐蚀，有利于平衡五效制盐蒸发系统和制硝蒸发系统。 4.本工艺采用循环硝水淘洗硝浆，有利于提高产品硝质量达到99.5%以上。 5.本工艺制硝系统简流程简化，有利于降低工程投资。 6.本工艺对原卤中含硝量变化的适应性强，有利于延长卤井的服务年限，本项目原则流程亦可适应硝盐联产。 7.本工艺蒸发系统热经济提高到3.35，能耗降低、盐硝产品质量高，技术经济指标领先国内外工艺水平，可增加产品的竞争力，具有较好的应用前景。 综上所述，循环法盐硝联产工艺对于NaCl-Na2SO4-H2O水盐体系可以经济合理的进行盐硝（或硝盐）联产分离。 参考文献 1.中国井矿盐1991年第6期“云应地区应用热法提硝工艺分析”彭赛军 2.中国井矿盐1995年第3期“盐硝联产兑卤循环法工艺流程探讨”彭赛军3.中国井矿盐2007年第1期“浅谈硫酸钠型卤水引进技术的设计特点及操作调控”张根祥、苏柏松4.中国井矿盐2007年第1期“对EV-302闪蒸罐结垢原因及防治的探讨”汤清军、邹志刚5.从Na2SO4-NaCl-H2O体系中生产硫酸钠和氯化钠的工艺（申请专利号200610114043.8） 2007年3月16日Co-Production of Salt and Nitre with Hot Recirculation Process of NaCl-Na2SO4-H2O SystemPeng Saijun(China BCEL International Engineering Co., Ltd. 100026 Beijing)Abstract: This paper studies co-production of salt and nitre with existing hot recirculation process of NaCl-Na2SO4-H2O brine and proposes the hot recirculation process for co-production of salt and nitre for reference by the engineers in the same trade in light with mixed brine recirculation process.Key words: Hot Recirculation Process, Co-production of Salt and NitreI. Study on the existing hot recirculation process for co-production of salt and nitreFor composition of rock salt mine sodium sulfate brine refer to table 1.Table 1 Composition of Sodium Sulfate BrineProducersUnitNaClNa2SO4CaSO4MgSO4H2OSino-Salt Zhenjiang Salt Mineg/l29013.863.640.33Jiangsu Huaerun Companyg/l30022.02.500.80Anhui Yangtze Salt Mineg/l28616.172.200.27Guangdong Longgui Salt Mineg/l28015.00.690.13Hunan Xiangfeng Salt Mineg/l30032.01.281.53Jiangxi Sale Mineg/l30025.01.600.80Hubei 728 Salt Mineg/l28817.32.510.65Sodium sulfate brine is of NaCl-Na2SO4-H2O system when it has negligible impurities. In the system, dissolubility of NaCl increases along with rising of temperature and dissolubility of Na2SO4 decreases along with rising of temperature when the ambient temperature is higher. Fore relevant data refer to table 2.Table 2 Relevant Data of NaCl-Na2SO4-H2O SystemTemperature CUnitNaClNa2SO4H2ORemarks150g/l34959808NaCl+Na2SO4105g/l31653841NaCl+Na2SO4100g/l30754849NaCl+Na2SO490g/l30854847NaCl+Na2SO475g/l30257850NaCl+Na2SO460g/l29863849NaCl+Na2SO455g/l29662852NaCl+Na2SO450g/l29365853NaCl+Na2SO445g/l28470857NaCl+Na2SO4According to the above law of dissolution of salt and nitre major existing processes of co-production of salt and nitre are:1. Salt out process of co-production of salt and nitreFor salt out process of co-production of salt and nitre refer to flow diagram figure 1. Vacuum SystemSteam I Effect II Effect III Effect IV Effect Mother LiquorSodium Sulfate Salt Separation Heating Heating Heating Salt Washing Sodium Chloride Salt Washing Mother Liquor Sodium Chloride BrineFigure 1 Flow Diagram of Hot Salt Out Process of co-production of Salt and NitreBoth feed of salt out mother liquor and discharge of salt are in co-current in the process. Salt slurry is discharged from the last effect of evaporator and the sodium sulfate in it is redissolved by mixing with ambient temperature brine. Washed salt becomes finished product salt after dewatering and drying. Salt washing mother liquor is heated up to 90C with condensate and secondary steam and sodium chloride is added for salt out. Finished product nitre is produced through salt out, nitre washing, dewatering and drying. For actual production data refer to table 3.Table 3 Production Data of Salt Out Process of Co-production of Salt and Nitre in Yunying Region in Hubei ProvinceItemsUnitCNaClNa2SO4CaSO4MgSO4H2ORaw brineg/l25270.526.461.521.05Settled matter of primary brine washing%3026.948.701.900.0662.4Salt washing brineg/l30285.2578.060.661.18Feed liquor to I effectg/l140311.054.520.330.29Feed liquor to II effectg/l125305.054.860.410.36Feed liquor to III effectg/l100306.756.580.211.09Feed liquor to IV effectg/l60304.256.360.215.45Salt washing mother liquorg/l90306.756.580.211.18Nitre after salt out%909.8250.4431.360.467.92Refined salt%7095.090.370.020.014.36According to the actual production situation main issues existing in the process which need to be resolved are:1) Concentration of sodium sulfate through brine mixing, lowering temperature and salt washing is limited by temperature and dissolubility. According to table 2, saturated dissolubility of sodium sulfate in brine is 80.8 g/l at ambient temperature and saturated dissolubility of sodium sulfate in brine is 52.0 g/l at 90C temperature. Theoretically, redissolution of sodium sulfate with raw brine washing salt and nitre slurry is limited when concentration of nitre is more than 30 g/l in raw brine.2) Scaling at pre-heating of salt washing brine and salt out: According to table 3, the process of pre-heating of salt washing brine and salt out is a process of dissolution of sodium chloride and separation of sodium sulfate and calcium sulfate. Application of secondary steam pre-heater is affected by scaling and frequent flushing.3) Separation of calcium and magnesium impurities from brine: According to table 3, calcium sulfate is separated out in the process of salt washing of brine and calcium sulfate and magnesium sulfate are separated out in the process of salt washing brine pre-heating and salt out. Calcium sulfate is separated out in the process of evaporation. Then, quality of sodium chloride and sodium sulfate products is affected.4) Application of four effects evaporation process impacts the economy of evaporation for salt making.Based on the existing process and progress of automation technology, adoption of the following measures can improve the relevant technical and economical indices.1) Brine purification process is used to remove calcium and magnesium impurities in raw brine and quality of sodium sulfate product can be improved to more than 99%.2) Adoption of five effects evaporators instead of four effect evaporators for salt making can improve the heat economy of evaporation system by more than 3.79%.3) Adoption of DCS automation system can control continuously and stably the production system and the annual effective production period can be more than 320 days.4) With purified brine salt washing and last effect mother liquor recirculation the quality of refined salt product can be improved to more than 99.1%.5) Instead of salt out for nitre separation, adoption of salt washing mother liquor evaporation for nitre separation is helpful to control the quality of sodium sulfate product.2. Imported evaporation process of co-production of salt and nitreFor imported evaporation process of co-production of salt and nitre refer to figure 2. Heating Heating Heating Purified Brine Vacuum SystemSteam 201 Salt Making 202 Salt Making 203 Salt Making 304 Salt Making Sodium ChlorideSteam 301 Nitre Making 302 Flashing Mother Liquor Nitre Out Mother Liquor Sodium Sulfate Heating HeatingFigure 2 Imported Evaporation Process Flow Diagram for Co-production of Salt and NitreIn the process, purified brine is fed in co-current through pre-heating with condensate and secondary steam and finished product salt is produced through evaporators of 201 to 304, salt discharge after washing with purified brine salt leg in horizontal flow, dewatering and drying. Salt making mother liquor is fed into 301 hot pump and nitre making evaporator after pre-heating with secondary steam from 302 flashing tank and 301 nitre making tank. Nitre product is produced through washing of nitre slurry with 304 salt making mother liquor, dewatering and drying. For relevant actual production data refer to table 4.Table 4 Production Data of Imported Evaporation Process of Co-production of Salt and Nitre with Sodium Sulfate BrineItemsUnitCOperation DataSaturated LiquorRemarksNaClNa2SO4NaClNa2SO4Purified brineg/l30300.015.0277.080.8201 feed liquorg/l107339.021.07306.054.3202 feed liquorg/l85.6329.029.85305.053.7203 feed liquorg/l63.3310.047.16299.058.2304 feed liquorg/l47.9296.062.29294.064.0301 feed liquorg/l98309.053.74307.053.7302 feed liquorg/l78.2305.053.97304.055.2Sodium sulfate%700.8099.0Refined salt%7099.50.20According to the actual production situation, due to the limit of compression ratio of thermal pump the unit area thermal transfer evaporation capacity is lower, the heating area is bigger and nitre making mother liquor flash tank 302 and salt making mother liquor pre-heaters 305 and 306 are apt to scaling for the adoption of thermal pump four effects evaporators for salt making. Based on the existing process and progress of automation technology the process and relevant technical and economical indices can be improved by taking the following measures:1) Nitre quality can be improved to more than 99.5% by using nitre water recirculation for nitre slurry washing.2) Instead of four effects evaporators, five effects evaporators are used to improve evaporation thermal economy to more than 3.79 for salt making.3) Elimination of thermal pump evapor