WO2023050565A1 - 一种针对高硬度低碳酸盐碱度煤气化灰水的电化学除硬方法 - Google Patents

一种针对高硬度低碳酸盐碱度煤气化灰水的电化学除硬方法 Download PDF

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WO2023050565A1
WO2023050565A1 PCT/CN2021/135562 CN2021135562W WO2023050565A1 WO 2023050565 A1 WO2023050565 A1 WO 2023050565A1 CN 2021135562 W CN2021135562 W CN 2021135562W WO 2023050565 A1 WO2023050565 A1 WO 2023050565A1
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electrochemical
gray water
treatment
water
hardness
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French (fr)
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朱田震
姚光源
章明歅
于德泽
陶蕾
何爱珍
王萌
胡兴刚
林志强
王堃
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中海油天津化工研究设计院有限公司
中海油能源发展股份有限公司
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    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F9/00—Multistage treatment of water, waste water or sewage
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
    • C02F1/4602—Treatment of water, waste water, or sewage by electrochemical methods for prevention or elimination of deposits
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
    • C02F1/461—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis
    • C02F1/46104—Devices therefor; Their operating or servicing
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
    • C02F1/5281—Installations for water purification using chemical agents
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/66—Treatment of water, waste water, or sewage by neutralisation; pH adjustment
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
    • C02F2103/34—Nature of the water, waste water, sewage or sludge to be treated from industrial activities not provided for in groups C02F2103/12 - C02F2103/32
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2201/00—Apparatus for treatment of water, waste water or sewage
    • C02F2201/46—Apparatus for electrochemical processes
    • C02F2201/461—Electrolysis apparatus
    • C02F2201/46105—Details relating to the electrolytic devices
    • C02F2201/46115—Electrolytic cell with membranes or diaphragms
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2301/00—General aspects of water treatment
    • C02F2301/08—Multistage treatments, e.g. repetition of the same process step under different conditions

Definitions

  • the invention relates to an electrochemical dehardening method for coal gasification ash water with high hardness and low carbonate alkalinity, belonging to the field of electrochemical dehardening.
  • coal chemical industry In recent years, my country's new coal chemical industry has developed rapidly, but each project has a large amount of water consumption and wastewater discharge, and most of them are concentrated in the northwest region where coal resources are abundant and water resources are scarce, often causing a series of environmental problems. Dealing with the shortage of water resources and pollution discharge in coal chemical industry is the top priority of coal chemical enterprises.
  • Coal gasification technology is one of the key processes of coal energy conversion. At present, this process mostly adopts mature coal-water slurry pressurized gasification technology. In some coal chemical enterprises in China, because the coal they use has a high ash melting point, in order to reduce the ash melting point of coal to adapt to the coal-water slurry pressurized gasification device, it is necessary to add limestone flux.
  • Limestone decomposes into calcium oxide at high temperature, and part of the calcium oxide reacts with silica and alumina in coal to lower the ash melting point of coal, and the remaining calcium oxide enters the gas washing water (black water).
  • the black water is treated by flocculation and sedimentation, and the discharged gray water has the typical characteristics of high hardness and low carbonate alkalinity.
  • the calcium ions in the water will inevitably be further concentrated, which will inevitably aggravate the scaling of the equipment. Whether it is from the perspective of equipment operation or the perspective of water quality itself, the difficulty of treatment will further increase. Therefore, it is very important to effectively remove hardness ions in the system in real time.
  • the main hard removal methods include conventional methods such as ion exchange resin method, membrane separation method, lime softening method, and drug addition method.
  • traditional alkali treatment carbon dioxide + sodium hydroxide, calcium hydroxide + sodium carbonate, etc.
  • this treatment method also introduces a large amount of sodium ions and carbonate ions into the medium, as well as acid ions such as chloride ions and sulfate ions introduced by adjusting the pH value, resulting in problems such as increased corrosion. Therefore, the development of high-efficiency dehardening technology suitable for gray water quality is of great significance to alleviate the scaling of coal gasification system and improve the water recovery rate of the system.
  • the electrochemical hardness removal technology has obvious environmental friendliness. Compared with the chemical method, this technology hardly introduces or introduces a small amount of foreign ions, which has attracted the attention of a large number of researchers at home and abroad in recent years. It mainly produces a high pH alkaline environment near the cathode through the electrolysis of water, promotes the transformation of bicarbonate to carbonate, and then increases the supersaturation of calcium carbonate in the local medium, promotes its crystallization, and finally reduces the concentration of water. hardness. In principle, the carbonate alkalinity in water is crucial for calcium hardness removal. However, as mentioned above, gasifier ash water tends to be characterized by high hardness and low carbonate alkalinity. It is especially necessary to introduce an appropriate amount of carbonate alkalinity in the electrochemical hard removal process.
  • Carbon dioxide is one of the most important emissions in coal chemical production. It is estimated that in 2020, domestic coal chemical enterprises will emit about 400 million tons of carbon dioxide. Introducing carbon dioxide into the electrochemical dehardening process of gray water to increase the carbonate alkalinity can not only improve the performance of electrochemical dehardening, but also has important environmental benefits.
  • the published patent CN107235564B aims at the electrochemical hardness removal treatment of low-carbonate alkalinity water quality, and proposes the method of adding carbon dioxide or air to improve the removal rate of calcium and magnesium hardness ions.
  • the invention is suitable for water with low hardness and low carbonate alkalinity, and does not need to add other chemicals to assist in removing hardness.
  • the total hardness value is mostly above 1000mg/L (calculated as calcium carbonate), and the content of inorganic carbon is often less than one-fifth of calcium hardness.
  • the acidity of water quality will gradually increase, resulting in a decrease in current efficiency, an increase in energy consumption, and cannot remove a sufficient amount of hardness ions, so it cannot meet the requirements of industrial applications.
  • the present invention provides a new type of dehardening method mainly based on diaphragm method electrolysis and supplemented by chemical method, which solves the problem of simple electrochemical dehardening method in the treatment of high hardness and low carbonate alkalinity coal gasification Low current efficiency, low hardness removal rate and high energy consumption in gray water.
  • the present invention is aimed at the electrochemical dehardening method of high hardness and low carbonate alkalinity coal gasification gray water, and is characterized in that, described electrochemical dehardening method comprises four steps in turn:
  • Alkali supplementation treatment add sodium hydroxide or potassium hydroxide to the cathode effluent of diaphragm electrolysis to increase the alkalinity of gray water;
  • Scale treatment introduce the alkaline gray water medium into the flocculation sedimentation tank, and undergo flocculation and sedimentation treatment to reduce the hardness of the gray water;
  • the order of the electrochemical treatment in step 2) and the alkali supplementation treatment in step 3) can be exchanged, that is, the order of the electrochemical treatment in step 2) and the alkali supplementation treatment in step 3) is first the electrochemical treatment and then the alkali supplementation treatment, or Electrochemical treatment is followed by alkali replenishment treatment; among them, electrolytic electrochemical treatment by diaphragm method is preferred.
  • the supplementary amount of carbon dioxide is determined by the relationship curve between the pH value of the medium and the content of inorganic carbon.
  • the method for measuring the relationship between the pH value and the inorganic carbon content is: adjusting the pH value by blowing carbon dioxide into the treatment medium, and then using the total alkalinity method to test the total inorganic carbon content of the medium under the conditions of each pH value ,get.
  • the alkalinity method is to stabilize the medium by adding an organic scale inhibitor to the gray water medium supplemented with carbon dioxide, then adding sodium hydroxide or potassium hydroxide to adjust the pH value at 8.45 to 9.5, and then pass hydrochloric acid
  • the alkalinity of methyl orange and phenolphthalein were measured by titration method. Based on the two alkalinity values and the non-carbonate alkalinity value of raw water, the inorganic carbon content in the medium was calculated.
  • the anode material of the diaphragm method electrolysis of the present invention is graphite, lead alloy, noble metal electrode or metal oxide coating electrode;
  • the cathode material is carbon steel, stainless steel, copper alloy, titanium alloy, graphite, lead alloy, noble metal electrode Or metal oxide coated electrodes;
  • the material of the diaphragm is cation exchange membrane, bipolar membrane, microporous ceramic membrane microporous plastic diaphragm, wood fiber diaphragm or asbestos diaphragm.
  • the cathode chamber of the diaphragm method electrolysis of the present invention processes the gray water medium supplemented with carbon dioxide or the gray water medium supplemented with carbon dioxide and sodium hydroxide or strong potassium oxide; the anode chamber processes the raw gray water medium.
  • the pH value of the effluent in the anode chamber is controlled above 5 by adjusting the gray water flow rate in the anode chamber; the pH value of the effluent water in the cathode chamber is adjusted by adjusting the gray water flow rate in the cathode chamber: After that, control the pH value of the cathode effluent to be between 8.5 and 9.5, and control the pH value of the cathode effluent to be above 10 when the alkali replenishment step is before the diaphragm electrolysis.
  • the cathode effluent after diaphragm electrolysis and alkali replenishment treatment flows into a catholyte post-treatment buffer tank containing calcium carbonate scale crystals, wherein the concentration of calcium carbonate scale crystals is stabilized at 10 to 60 g/L , fully stirred for 20-120s, flowed into the flocculation settling tank, flocculated and precipitated to remove scale, and the softened supernatant entered the gray water system.
  • the beneficial effect of the present invention is: using the carbon dioxide discharged from the coal chemical industry to rationally add inorganic carbon to the high hardness and low carbonate alkalinity coal gasification ash water, adopting the diaphragm electrolysis method as the main method and alkali supplementation as the auxiliary method to improve the electricity
  • the effect of chemical hardness removal rate and reduce energy consumption so as to alleviate the system scaling problem of coal gasification system, and realize water saving and emission reduction of coal gasification system.
  • Fig. 1 is a kind of embodiment of the present invention coal gasification ash water electrochemical dehardening process flow chart
  • Fig. 2 is the figure of the influence of adding carbon dioxide on the total inorganic carbon content of the medium
  • Figure 3 is the effect of adding carbon dioxide (medium pH) on the hard removal effect.
  • the electrochemical dehardening process of the present invention includes gray water tank 1, gas-liquid mixing pump 2, cathode pretreatment liquid buffer tank 4 in sequence according to the direction of water flow , electrolytic cell 6, catholyte post-treatment buffer tank 11 and flocculation settling tank 14.
  • the relationship curve between the pH value of the coal gasification gray water and the content of inorganic carbon is measured by the alkalinity method: first, carbon dioxide is blown into the coal gasification gray water to adjust to different pH values; Add organic antiscalant to the water sample to stabilize the medium, then add sodium hydroxide to adjust its pH value to 8.5, and then obtain the alkalinity of methyl orange and phenolphthalein through hydrochloric acid titration, based on the two alkalinities and the raw water non-carbon The acid alkalinity value is calculated to obtain the inorganic carbon content in the medium, and finally the pH-inorganic carbon content curve is obtained.
  • the pH value of the coal gasification gray water mixed with gas and liquid is regulated by adjusting the carbon dioxide intake volume of the gas-liquid mixing pump 2 (supplied by the carbon dioxide storage tank 3) (measured by a pH value monitor 15), so as to obtain gray water with different inorganic carbon contents.
  • the electrolytic cell 6 is a diaphragm electrolytic cell, wherein the diaphragm 10 adopts an oxidation-resistant sulfonic acid type cation exchange membrane, the cathode 8 adopts a titanium mesh, and the anode 9 adopts a titanium-based ruthenium-iridium oxide-coated electrode mesh; A constant current and voltage stabilized power supply 7 is provided.
  • the medium to be treated flows in and out from the bottom in the cathode and anode chambers; the cathode effluent flows into the catholyte post-treatment buffer tank 11, and the anode effluent returns to the gray water tank 1; the cathode treatment medium is gray water medium supplemented with carbon dioxide; Add carbon dioxide to the gray water medium, and adjust the pH value of the effluent from the anode chamber to above 4 by changing the flow rate.
  • the cathode chamber effluent flows into the catholyte post-treatment buffer tank 11, wherein the calcium carbonate scale crystal concentration is stable at 10-60 g/L, and the scale crystal grain size is below 1000 ⁇ m; add sodium hydroxide concentrate (provided by the concentrated alkali tank 12) therein , the pH value (measured by the pH value monitor II 13) is adjusted to more than 10, and after fully stirring for 20 to 120s simultaneously, the treatment solution containing suspended scale crystal microparticles is introduced into the flocculation-settling tank 14, and processed through further flocculation and sedimentation, The softened supernatant and the effluent from the anode chamber are mixed and then flowed back into the gray water tank 1 .
  • the ash water volume of the gasifier in a coal chemical enterprise is 1000m 3 /h, and the physical and chemical parameters of the water quality are shown in Table 1.
  • the gray water medium with a flow rate of 100L/h is drawn from the gray water tank, and the method of the invention is used for softening treatment.
  • the electrochemical hardness removal device 6 of the present invention is used to treat raw water.
  • Table 2 When the pH value of the cathode chamber can reach more than 11, the hardness removal rate, current efficiency and hardness removal rate of the device are still lower than those of conventional diaphragms.
  • the electrochemical hardening effect, and the energy consumption of the device is above 50Kw.h/kg CaCO 3 , which cannot meet the softening requirements.
  • the gas-liquid mixing pump 1 is used to add different amounts of carbon dioxide to the cathode pretreatment liquid buffer tank 4 to obtain gray water quality with different pH values.
  • the relationship curve between the inorganic carbon content and pH value in the medium is measured by the alkalinity method as shown in the figure 2.
  • Electrochemical hardness removal treatment was performed on gray water with various pH values. The results are shown in Figure 3. It can be seen that the hardness removal rate and current efficiency of the device are significantly improved, and when the pH value is around 5.8, the inorganic carbon content in the medium (TIC ) is equivalent to the total hardness, at this time the hardening effect is the best, the hardening rate reaches 60%, the current efficiency reaches 50%, and the energy consumption drops to around 15Kw.h/kg CaCO 3 .
  • the electrochemically treated gray water is further treated with alkali supplementation.
  • Sodium hydroxide is added to the catholyte post-treatment buffer tank 11 to increase the pH value from 9 to 10.8, and the residence time is 1 min at the same time. After fully stirring and crystallizing, the total hardness of the treated water is 4.05 mmol/L, which is reduced by about 75%. .
  • the suspended gray water after dehardening flows into the flocculation settling tank 14, and the scale crystals in the medium are quickly removed through flocculation and sedimentation treatment, and the supernatant and diaphragm electrolyzer 6 anode chamber effluent (regulate the anode gray water flow rate to adjust the pH value) Near 4.8 of the control) backflow into gray water tank 1 after mixing.

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  • Hydrology & Water Resources (AREA)
  • Engineering & Computer Science (AREA)
  • Environmental & Geological Engineering (AREA)
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Abstract

一种针对高硬度低碳酸盐碱度煤气化灰水的电化学除硬方法。该方法依次包括：1)向灰水中补加二氧化碳，使得无机碳摩尔量是钙摩尔量的0.8～1.2倍；2)采用隔膜法电解对灰水进行电化学处理；3)补碱处理提升灰水碱性；4)沉垢处理，将碱性灰水介质引入絮凝沉降槽中，经絮凝沉降处理，以此降低灰水硬度。本方法利用煤化工排放的二氧化碳向高硬度低碳酸盐碱度煤气化灰水中补加无机碳，采用隔膜法电解为主、补碱为辅的电化学除硬方法，提升电化学除硬效果、降低能耗，缓解了煤气化系统的结垢问题，实现煤气化系统节水减排。

Description

一种针对高硬度低碳酸盐碱度煤气化灰水的电化学除硬方法 技术领域
本发明涉及一种针对高硬度低碳酸盐碱度煤气化灰水的电化学除硬方法，属于电化学除硬领域。
背景技术
近年来我国新型煤化工发展迅速，但各项目都具有较大的耗水量和废水排放量，且大都集中在煤资源丰富、水资源短缺的西北地区，往往导致一系列环境问题。处理好煤化工水资源短缺及污染排放问题是煤化工企业的重中之重。煤气化技术是煤炭能源转化的关键工艺之一，目前该工艺多采用成熟的水煤浆加压气化技术。在国内的一些煤化工企业，由于其使用的煤种灰熔点高，为降低煤的灰熔点以适应水煤浆加压气化装置，需加入石灰石助熔剂。石灰石在高温下分解成氧化钙，部分氧化钙与煤中的二氧化硅、氧化铝等反应，降低了煤的灰熔点，剩余的氧化钙进入煤气洗涤水(黑水)中。这些黑水经絮凝沉淀处理，排出的灰水多具有高硬度低碳酸盐碱度的典型特征。针对该水质，若减小排污量，水中的钙离子必然进一步浓缩，势必加剧设备结垢，无论是从设备运行角度，还是从水质本身的角度，治理难度将进一步增大。因此，实时有效去除系统中的硬度离子至关重要。目前主要的除硬方法有离子交换树脂法、膜分离法、石灰软化法、加药法等常规手段。针对灰水水质，传统的加碱处理(二氧化碳+氢氧化钠，氢氧化钙+碳酸钠等)较为普遍。尽管如此，该处理方法在除去硬度离子的同时，还向介质中引入大量的钠离子、碳酸根离子，以及回调pH值引入的氯离子、硫酸根等酸根离子，导致腐蚀加剧等问题。因此，开发适用于灰水水质的高效除硬技术，对缓解煤气化系统结垢，提高系统水回收率，具有重要意义。
电化学除硬技术具有明显的环境友好性，相比化学法除硬，该技术几乎不引入或者少量引入外来离子，近年来引起国内外大量研究者的关注。其主要是通过水的电解反应在阴极附近产生高pH值碱性环境，促进碳酸氢根向碳酸根的转变，进而提升局部介质中碳酸钙的过饱和度，促进其结晶析出，最终降低水的硬度。从原理上来讲，水中碳酸盐碱度对钙硬去除至关重要。然而如上所述，气化炉灰 水往往具有高硬度低碳酸盐碱度的特征。在电化学除硬流程引入适量的碳酸盐碱度尤为必要。
二氧化碳是煤化工生产中最主要的排放气体之一，据估算，2020年国内煤化工企业排放的二氧化碳达到4亿吨左右。将二氧化碳引入灰水的电化学除硬工艺以提升碳酸盐碱度，不但可提升电化学除硬性能，而且具有重要的环保效益。公开专利CN107235564B针对低碳酸盐碱度水质的电化学除硬处理，提出补加二氧化碳或者空气的方法，来提升钙、镁硬度离子的去除率。该发明适用于低硬度低碳酸盐碱度水质，且无需补加其他药剂辅助除硬。尽管如此，对于煤气化灰水，总硬度值大多在1000mg/L(以碳酸钙计)以上，而无机碳含量往往不及钙硬度的五分之一，在补加二氧化碳基础上，单纯靠电化学，在除硬的过程中，水质酸性会逐渐增强，导致电流效率下降，能耗增大，且无法无法去除足够量的硬度离子，因此不能满足工业应用要求。
发明内容
本发明针对现有技术存在的不足，提供一种以隔膜法电解为主、化学法为辅的新型除硬方法，解决了单纯电化学除硬法在处理高硬度低碳酸盐碱度煤气化灰水时电流效率低、除硬率低、能耗高的问题。
本发明解决上述技术问题的技术方案如下：
本发明针对高硬度低碳酸盐碱度煤气化灰水的电化学除硬方法，其特征在于，所述的电化学除硬方法依次包括四个步骤：
1)补加二氧化碳：首先向灰水中补加二氧化碳，使得无机碳摩尔量是钙摩尔量的0.8～1.2倍；
2)电化学处理：采用隔膜法电解对灰水进行电化学处理；
3)补碱处理：向隔膜电解阴极出水中补加氢氧化钠或氢氧化钾，提升灰水碱性；
4)沉垢处理：将碱性灰水介质引入絮凝沉降槽中，经絮凝沉降处理，以此降低灰水硬度；
其中，步骤2)的电化学处理和步骤3)的补碱处理顺序可调换，即步骤2)的电化学处理和步骤3)的补碱处理的顺序为先电化学处理后补碱处理，或先补碱处理后电化学处理；其中优选隔膜法电解电化学处理在前。
本发明所述的电化学除硬方法中，优选，所述二氧化碳补加量是通过介质pH 值和无机碳含量的关系曲线来确定。
优选，所述pH值和无机碳含量关系曲线测量方法是：通过在处理介质中鼓入二氧化碳以调节其pH值，然后在各pH值条件下，采用总碱度法测试介质的总无机碳含量，获得。优选，所述碱度法是通过向补加二氧化碳的灰水介质中投加有机阻垢剂以稳定介质，然后向其中加入氢氧化钠或氢氧化钾调节pH值在8.45～9.5，然后通过盐酸滴定法测法测得甲基橙碱度和酚酞碱度，基于两种碱度值及原水非碳酸盐碱度值，计算得出介质中的无机碳含量。
优选，本发明所述的隔膜法电解的阳极材质为石墨、铅合金、贵金属电极或金属氧化物涂层电极；阴极材质为碳钢、不锈钢、铜合金、钛合金、石墨、铅合金、贵金属电极或金属氧化物涂层电极；隔膜材质为阳离子交换膜、双极膜、微孔陶瓷膜微孔塑料隔膜、木质纤维隔膜或者石棉隔膜。
本发明所述隔膜法电解的阴极室处理补加二氧化碳的灰水介质或者处理补加二氧化碳并补加氢氧化钠或强氧化钾的灰水介质；阳极室处理原灰水介质。
优选，所述隔膜法电解过程中，通过调节阳极室灰水流量将其出水pH值控制在5以上；通过调节阴极室灰水流量来调节阴极室出水pH值：当补碱步骤在隔膜法电解之后时，控制阴极出水pH值在8.5到9.5之间，当补碱步骤在隔膜电解之前时，控制阴极出水pH值在10以上。
优选，本发明所述的沉垢过程，经隔膜电解和补碱处理后的阴极出水，流入含碳酸钙垢晶的阴极液后处理缓冲罐，其中碳酸钙垢晶浓度稳定在10～60g/L，充分搅拌20～120s，流入絮凝沉降槽，经絮凝沉淀去除垢渣，软化后的上清液进入灰水系统。
本发明的有益效果是：利用煤化工排放的二氧化碳向高硬度低碳酸盐碱度煤气化灰水中合理补加无机碳，采用隔膜法电解为主、补碱为辅的除硬方法，提升电化学除硬率效果、降低能耗，以此缓解煤气化系统的系统结垢问题，并实现煤气化系统节水减排。
附图说明
图1为本发明的一种实施例煤气化灰水电化学除硬工艺流程图；
图2为补加二氧化碳对介质总无机碳含量的影响图；
图3为补加二氧化碳(介质pH)对除硬效果的影响。
其中，1、灰水槽；2、气液混合泵；3、二氧化碳储罐；4、阴极预处理液缓冲罐；5、pH值监测器I；6、电解槽；7、稳流稳压电源；8、阴极；9、阳极；10、隔膜；11、阴极液后处理缓冲罐；12、浓碱罐；13、pH值监测器II；14、黑水沉降槽。
具体实施方式
下面结合具体实施例对本发明新型高硬度低碳酸盐碱度煤气化灰水电化学除硬技术方案做进一步描述。
如图1所示，针对高硬度低碳酸盐碱度煤气化灰水，本发明的电化学除硬工艺按照水流方向依次包括灰水槽1、气液混合泵2、阴极预处理液缓冲罐4、电解槽6、阴极液后处理缓冲罐11和絮凝沉降槽14。
处理煤气化灰水之前，先通过碱度法测得煤气化灰水pH值和无机碳含量关系曲线：首先向煤气化灰水中鼓入二氧化碳，调至不同pH值；然后向各煤气化灰水水样中添加有机阻垢剂以稳定介质，然后补加氢氧化钠调节其pH值为8.5，然后通过盐酸滴定得出甲基橙碱度和酚酞碱度，基于两种碱度及原水非碳酸盐碱度值计算得出介质中的无机碳含量，最终得出pH-无机碳含量曲线。基于该曲线，在灰水进液量为定值的条件下，通过调节气液混合泵2的二氧化碳进气量大小(由二氧化碳储罐3供给)调控气液混合的煤气化灰水的pH值(通过pH值监测器I 5测得)，以此获得不同无机碳含量的灰水。
电解槽6为隔膜电解槽，其中隔膜10采用耐氧化的磺酸型阳离子交换膜，阴极8采用钛网，阳极9采用钛基钌铱氧化物涂层电极网；装置运行过程中，电解电流由稳流稳压电源7提供。被处理介质在阴、阳极室均为下进上出流向；阴极出水流入阴极液后处理缓冲罐11，阳极出水返回灰水槽1；阴极处理介质为补加二氧化碳的灰水介质；阳极介质采用未补加二氧化碳的灰水介质，通过改变流量将阳极室出水pH值调至4以上。
阴极室出水流入阴极液后处理缓冲罐11，其中碳酸钙垢晶浓度稳定在10～60g/L，垢晶粒径在1000μm以下；向其中补加氢氧化钠浓液(浓碱罐12提供)，将pH值(通过pH值监测器II 13测得)调至10以上，同时充分搅拌20～120s后，将含悬浮垢晶微颗粒的处理液引入絮凝沉降槽14，经进一步絮凝沉降处理，将软化的上清液和阳极室出水混合后回流进入灰水槽1。
某煤化工企业气化炉灰水量1000m 3/h，水质物化参数见表1所示。基于其高硬度低碳酸盐碱度的水质特征，从灰水槽引出100L/h流量的灰水介质，采用本发明方法进行软化处理。首先采用本发明电化学除硬装置6对原水进行处理，结果如表2所示，当阴极室出pH值可达到11以上，装置除硬率、电流效率及除硬速率均仍低于常规隔膜电化学除硬效果，且装置能耗在50Kw.h/kg CaCO 3以上，这些都无法满足软化要求。
采用气液混合泵1向阴极预处理液缓冲罐4中补加不同量二氧化碳，获得不同pH值的灰水水质，通过碱度法测得该介质中无机碳含量和pH值的关系曲线如图2所示。对各pH值的灰水进行电化学除硬处理，结果如图3所示，可以看到装置除硬率、电流效率均明显提升，且当pH值在5.8附近，介质中无机碳含量(TIC)与总硬度相当，此时除硬效果最佳，除硬率达到60％，电流效率达到50％，且能耗降至15Kw.h/kg CaCO 3附近。
在上述最佳二氧化碳补加量条件下，对经电化学处理的灰水做进一步补碱处理。向阴极液后处理缓冲罐11中补加氢氧化钠，将pH值从9提升至10.8，同时停留时间1min，经充分搅拌结晶，处理后的水质总硬度为4.05mmol/L，降低约75％。被除硬后的悬浊灰水，流入絮凝沉降槽14，经絮凝沉淀处理，快速将介质中的垢晶去除，上清液和隔膜电解槽6阳极室出水(调控阳极灰水流量将pH值控制的4.8附近)混合后回流进入灰水槽1。
进一步将本发明与纯电化学及化学法的处理成本进行对比，如表3所示，针对高硬度低碳酸盐碱度煤气化灰水，本发明除硬方法的处理成本最低，约为4.34元/m 3，技术优势明显。
表1灰水水质物化参数
Figure PCTCN2021135562-appb-000001
表2针对灰水原水的电化学除硬效果
Figure PCTCN2021135562-appb-000002
表3几种除硬法处理成本对比
Figure PCTCN2021135562-appb-000003
以上所述仅为本发明的较佳实施例，并不用以限制本发明，凡在本发明的精神和原则之内，所作的任何修改、等同替换、改进等，均应包含在本发明的保护范围之内。

Claims (7)

  1. 一种针对高硬度低碳酸盐碱度煤气化灰水的电化学除硬方法，其特征在于，所述的电化学除硬方法依次包括如下步骤：
    1)补加二氧化碳：首先向灰水中补加二氧化碳，使得无机碳摩尔量是钙摩尔量的0.8～1.2倍；
    2)电化学处理：采用隔膜法电解对灰水进行电化学处理；
    3)补碱处理：向隔膜电解阴极出水中补加氢氧化钠或氢氧化钾，提升灰水碱性；
    4)沉垢处理：将碱性灰水介质引入絮凝沉降槽中，经絮凝沉降处理，以降低灰水硬度；
    其中，步骤2)的电化学处理和步骤3)的补碱处理的顺序为先电化学处理后补碱处理，或先补碱处理后电化学处理。
  2. 根据权利要求1所述的电化学除硬方法，其特征在于，所述二氧化碳补加后灰水介质中无机碳含量确定方法是通过在处理介质中鼓入二氧化碳以调节其pH值，然后在各pH值条件下采用总碱度法测试介质的总无机碳含量得到pH值和无机碳含量的关系曲线后获得。
  3. 根据权利要求2所述的电化学除硬方法，其特征在于，所述二氧化碳补加后灰水介质中无机碳含量确定方法包括：首先通过向不同二氧化碳补加量灰水介质中添加有机阻垢剂以稳定水质，然后向添加了有机阻垢剂的灰水介质中加入氢氧化钠或氢氧化钾，将其pH值调至在8.45～9.5，再通过盐酸滴定法测得甲基橙碱度和酚酞碱度，基于两种碱度值及原水非碳酸盐碱度值，计算出介质中的无机碳含量，进而得出pH值和无机碳含量的关系曲线，基于该曲线，确定二氧化碳补加量。
  4. 根据权利要求1所述的电化学除硬方法，其特征在于，所述隔膜法电解用的阳极材质为石墨、铅合金、贵金属电极或金属氧化物涂层电极；阴极材质为碳钢、不锈钢、铜合金、石墨、钛合金、铅合金、贵金属电极或金属氧化物涂层电极；隔膜材质为阳离子交换膜、双极膜、微孔陶瓷膜、微孔塑料隔膜、木质纤维隔膜或者石棉隔膜。
  5. 根据权利要求1所述的电化学除硬方法，其特征在于，所述隔膜法电解的阴极室处理补加二氧化碳的灰水介质或者处理补加二氧化碳并补加氢氧化钠或氢氧化钾的灰水；阳极室处理原灰水。
  6. 根据权利要求1所述的电化学除硬方法，其特征在于，所述步骤2)电化学处理中，通过调节阳极室灰水流量使其出水pH值控制在4以上；通过调节阴极室灰水流量调节阴极室出水pH值：当补碱处理步骤在电化学处理步骤之后时，控制阴极出水pH值在8到9.5之间，当补碱处理步骤在电化学处理步骤之前时，控制阴极出水pH值在10以上。
  7. 根据权利要求1所述的电化学除硬方法，其特征在于：所述灰水经电化学处理和补碱处理后的阴极出水，流入阴极液后处理缓冲罐，其中含有碳酸钙垢晶10～60g/L，垢晶粒径在1000μm以下，搅拌20～120s后流入絮凝沉降槽，经絮凝沉淀去除垢渣，软化后澄清灰水和电化学处理的阳极出水混合回流进入灰水系统。
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