Study On Silicon Removal Technology Of Heavy Oil Production Water By Chemical Coagulation

As a common mining method of heavy oil,hot recovery will produce a large amount of produced water containing certain heat energy during mining.The produced water will be reused in hot recovery boilers,which can not only make full use of the heat energy of produced water,but also save fresh water resources and protect the environment.However,in the actual application process,due to the high silicon content of heavy oil produced water,direct reuse of hot recovery boilers will lead to scale formation of gas pipelines and boilers,which will lead to pipeline damage and even boiler explosion in serious cases.For the above reasons,produced water needs to be silicon removed before it is reused into boilers.There are many commonly used silicon removal technologies,among which chemical coagulation technology is used as the main silicon removal means for heavy oil produced water treatment due to its low cost and simple operation.In this thesis,the produced water of a sewage treatment station in Liaohe River is taken as the main research object,based on the existence modes of reactive silicon and non-reactive silicon in water.The interaction between reactive silicon and non-reactive silicon under the influence of temperature,pH,anion and metal cation was investigated.The desilication effect of ferric sulfate,aluminum sulfate,magnesium sulfate,calcium chloride and other agents under the influence of pH,temperature and dosage was carried out.The conditions of the superior desilication effect were screened out.The orthogonal experiment was conducted to determine the better desilication effect,and the main action mechanism of chemical coagulation desilication was clarified.The results show that the reactive silicon content increases and the non-reactive silicon content decreases with the increase of temperature.When pH is less than 8,the content of reactive silicon is low;when pH is greater,the silicic acid is gradually decomposed into silicic acid,and the non-reactive silicon is depolymerized into silicic acid under alkaline condition,and the content of reactive silicon rises quickly.Anions have no effect on the content of reactive silicon,while the effects of cationic calcium and magnesium ions and manganese ions vary significantly with pH.It can be analyzed that these metal ions produce silicate precipitation as the main role.The changes of iron,aluminum and zinc ions are not obvious.Under alkaline conditions,the contents of iron,aluminum and zinc ions are less,which are mainly caused by catalysis and salting-out.The silicon removal study shows that the effect of removing silicon is better when the pH of iron is 4.0,the concentration of iron sulfate is 2000mg·L^-1 and the temperature is 60℃.After the treatment,the silicon content is reduced to 45.4mg·L^-1.The principle of removing silicon is mainly flocculation and removal of non-reactive silicon,and the reactive silicon is removed through the catalytic action of iron ion.When pH of aluminum agent is 7.0,concentration of aluminum sulfate is 1500mg·L^-1,and temperature is 60℃,the silicon removal effect is the best.After treatment,the silicon content is reduced to 0.8mg·L^-1.The principle of silicon removal is to form flocculent to remove non-reactive silicon,and the reactive silicon is mainly removed by salting out aluminum salt.When the pH of magnesium agent is 10.4,the dosage of magnesium agent is 1500mg·L^-1,and the temperature is 80℃,the effect of removing silicon is the best.After treatment,the silicon content is reduced to 17.8mg·L^-1.The principle of removing silicon is that magnesium ion forms magnesium silicate precipitation with reactive silicon.The silicon removal principle of calcium agent is calcium ion and reaction silicon to generate calcium silicate precipitation,but with the increase of temperature,the concentration of calcium ion in water decreases,can not be used as the main silicon removal agent.A large amount of silica-containing sludge is produced after the removal of silicon from heavy oil production water.After XRF analysis,the results show that in the sludge,the content of hazardous heavy metals is lower than the detection limit.After the sludge was dissolved,the atomic absorption spectrophotometry was used to detect the cadmium content.The results showed that the cadmium content exceeded the control value of agricultural soil pollution risk,and the application to agricultural soil had serious safety risks.The content of chromium in the sludge treated with iron agent exceeds the control value of soil pollution risk of construction land,and there are hidden dangers.Further risk assessment of the sludge produced by desilication is required before it can be put into use.