Design Of Coke Oven Flue Gas Purification System Based On DCS

According to the requirements of national environmental protection administration and relevant flue gas emission standards of coking industry,SO₂ and NO_x in the flue gas discharged by coking plant can only be discharged into the atmosphere after desulfurization and denitration.In this paper,a coke oven flue gas desulfurization and denitrification project is designed for a coking plant.Two sets of flue gas desulfurization and denitrification and waste heat recovery facilities with a scale of 250000m³/h are newly built to deal with the flue gas discharged from four 55 hole 5.5m stamp charging coke ovens of the company.According to the principles of safety,reliability,economy and applicability,multiple schemes are selected and compared.The advanced,mature and reliable denitrification technology is selected before operation Desulfurization process technology,including selective catalytic reduction?SCR?for denitration technology and magnesium flue gas desulfurization technology,the core technology of which is absorption tower design,as well as other supporting devices,such as waste heat recovery system,magnesium sulfate recovery system,etc.Yokogawa DCS is selected as the control system.In the analog quantity control of denitration system,the main control contents include:water temperature control of liquid ammonia evaporator,pressure control of ammonia buffer tank,ammonia injection flow control of SCR reactor,flow control of dilution fan,constant value control of NO_x at the outlet,ammonia pressure control of ammonia buffer tank,etc.in the ammonia injection flow control of SCR reactor,I designed to use fixed mole ratio Carry out PID feedback control;the design of liquid ammonia evaporator water temperature control is to use the size of deviation value to adjust the opening of temperature regulating valve,and use PID in DCS central processor to control;the design of ammonia pressure control of ammonia buffer tank is to use single loop PID control system to control the valve position output of pressure regulating valve.In addition,liquid ammonia provides ammonia for SCR denitration reaction.Due to the special physical and chemical properties of ammonia,a series of interlocking procedures are set up in the ammonia area to ensure the safety of the ammonia area.There are many factors that affect the effect of flue gas desulfurization,such as pH value of slurry,mg/S ratio,flue gas flow,SO₂ concentration in flue gas,liquid gas ratio?L/G?,etc.in the pH control of absorption tower,the design considers to control pH within a certain range by adjusting the opening of magnesium hydroxide slurry valve through feedforward control;in the liquid level control of absorption tower,automatic control and manual control are designed There are two ways to start and stop the pump by dynamic control to achieve free switching.The author mainly made the determination of basic process parameters,the selection of catalyst,the selection of denitration system and desulfurization system equipment,the selection of instruments,the selection of automatic control system,hardware configuration,the programming of denitration part control system and desulfurization part control system.After debugging,the project has been put into normal production.Compared with before the device was used,the desulfurization efficiency increased by 90%and the denitrification efficiency increased by 85%.The control effect is good and the standard emission of coking gas is achieved.