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The flue gas denitration technology of liquid ammonia tank level gauge

by:Sincerity     2021-01-16
Liquid ammonia is widely used in many industries, such as coal-fired power plants, steel mills, such as flue gas denitration process is common in ammonia method denitration process nitrogen can be used in preparation by liquid ammonia evaporation. Liquid ammonia is a kind of important chemical raw materials, flammable and toxic substances, easy to bath in water under atmospheric pressure. For transportation and storage convenience, will usually gaseous ammonia liquid ammonia is obtained by compression or cooling way, stored in the pressure cylinder or tank, the storage tank of liquid ammonia dosage can be monitoring by liquid level detection. This article will combine flue gas denitration processing section for a certain steel works has been put into operation station of the liquid ammonia, discuss the liquid ammonia tank level gauge selection, in the process of the liquid level meter installation and matters needing attention. 1. Liquid ammonia stand introduction liquid ammonia in the flue gas denitration process station is for the purpose of the preparation of gaseous ammonia production, the main equipment are liquid ammonia unloading compressor, liquid ammonia tank, liquid ammonia evaporator, ammonia buffer tank, dilute ammonia tank, waste water pool, and form a complete set of pumps, valves, piping accessories (such as FIG. 1) 。 By the liquid ammonia tank lorry transport supply of liquid ammonia tank lorry with ammonia storage system connection with crane pipe unloading arm, using unloading compressor within the liquid ammonia liquid ammonia tank by the tanker input: using the liquid ammonia tank of liquid nitrogen and liquid nitrogen pressure difference between the evaporator and its own gravitational potential energy will supply to the liquid ammonia liquid ammonia 気 within Cai Faqi ammonia evaporation. As can be seen from the above process of liquid nitrogen storage tank of liquid nitrogen station storage devices, in liquid ammonia station equivalent ー materials center, is responsible for the production of ammonia gas repository of raw materials. In accordance with the 'technical specification for design of thermal power plant flue gas denitration, liquid ammonia station designed for fire danger b grade, so need to consider the explosion-proof electrical equipment in the area. Reference 'fixed pressure vessel safety technology and supervision code' to select the equipment of explosion-proof type: the explosion of the liquid ammonia station medium composition for ammonia, level gauge of explosion-proof type whether choose this Ann type or flameproof, can in principle. According to the specification, explosion-proof category for Ⅱ class ( Factories use electrical equipment) , explosion-proof level for class A, temperature classes T1. 2. Selection of liquid ammonia tank as pressure vessel in the fire, explosion and gas has many requirements. In accordance with the 'technical specification for design of thermal power plant flue gas denitration, liquid ammonia tank is usually used in normal temperature full pressure, horizontal steel structure, the design of the tank pressure 2. 16 mpa, tank is made of low alloy steel. Tank manhole, front-rear tube, gas discharge pipe, gas phase balance pipe, drainage pipe and equipment such as safety relief valve and the table will need to be equipped with pressure gauge, thermometer and the level device such as a safety inspection. In industrial process control, the selection of the liquid level test in general need to consider the following factors: 1) According to the measuring range, need to consider the measurement precision and measurement function selection; 2) The physical and chemical properties and state of the measured medium, such as ph value, viscosity, whether its solidification and gasification, etc. ; 3) The change of operating conditions, such as medium temperature, pressure, concentration and density change; 4) The container object structure, shape, size, container equipment accessories and various front-rear nozzle should be considered; 5) Measuring instrument in the face of the environment, such as the existence of flammable, toxic and explosion danger, and the environment temperature, etc. 2. 1 in a flue gas denitration analyzing characteristics of the liquid ammonia tank processing section has been put into operation of liquid ammonia station construction have 3 liquid ammonia tank, each ZUI large storage capacity of 107 m3 storage tank, the structure form of horizontal tank ( FIG. 2) This project of liquid ammonia tank to let stand horizontal tank, analyzes its working condition can be seen: 1) Work of liquid ammonia storage tank pressure is 1. 5 mpa, temperature is 25 ℃, relative dry at medium, exist within the tank in the form of gas liquid two phase, the upper exist in gas phase, liquid ammonia non-corrosive and adhesive itself, but in case of water will absorb quickly generated ammonia, corrosive. 2) Tank liquid level fluctuation range is not big, in the measurement of liquid medium and no other equipment in the area of dynamic resistance. 2. 2 selection plan according to the working characteristics of the liquid ammonia tank, several kinds of common material level detection instrument can be used, such as differential pressure type level gauge, magnetic level gauge, capacitive liquid level meter and radar level gauge (turning Including guided wave radar level gauge, etc. ) 。 But the liquid ammonia tank is a pressure vessel, has its special requirement on the liquid level detection. According to the fixed pressure vessels safety technology supervision regulation of regulation: to extreme used in explosive, toxic, highly harmful medium liquefied gas pressure vessel, prevent leakage protection device. Want to accord with the requirement of liquid level detection scheme is relatively limited. Due to large storage tank volume of this project, adopted two kinds of solution to detect the liquid level: in view of the scene shows in the level of using the magnetic level gauge (turning The level gauge) And need to signal remote control room of the liquid level detection flange differential pressure transducer was used to measure Far eastone level gauge) 。 Considering the maintenance point of view.
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