Valve selection and replacement precautions Valve selection and installation of waste heat generation system
The importance of valve selection adjustment valve structure selection is based on the use of the medium, temperature, pressure before and after the valve, flow, physical and chemical properties of the medium and the degree of media cleanliness factors such as comprehensive consideration to decide. Valve structure selection of correctness and rationality, directly related to the use of performance, regulating performance, regulating stability, and service life.
The importance of valve selection
The selection of the valve structure is based on the use of the medium, temperature, pressure before and after the valve, flow, physical and chemical properties of the medium and the clean degree of the medium and other factors. Valve structure selection of correctness and rationality, directly related to the use of performance, regulating performance, regulating stability, and service life.
Valve selection needs to be implemented working condition information
I. Process parameters:
1. Medium name.
2, medium density, viscosity, temperature, medium cleanliness (with particulate matter).
3, physical and chemical properties of the medium: such as corrosion, toxicity, acid and alkaline.
4, medium flow: relatively large, normal, small.
5, the medium valve before, after the valve pressure: relatively large, normal, small.
6. Medium viscosity, the greater the viscosity, the more the Cv value of the calculation.
These PARAMETERS ARE USED TO CALCULATE THE SIZE OF THE VALVE, THE RATED Cv VALUE, AND THE APPROPRIATE MATERIALS FOR THE VALVE.
Two, functional parameters:
1. Mode of action: electric, pneumatic, electro-hydraulic, hydraulic.
2, valve function: regulation, cut off, regulation and cut off sharing.
3, control mode: positioner, solenoid valve, pressure reducing valve.
4. Action time requirements.
This part of the parameters are mainly used to determine the functional requirements of the valve need to be configured with some accessories.
Three, explosion-proof protection parameters:
1, explosion-proof grade.
2. Protection level.
4. Environment and dynamic parameters:
1. Ambient temperature.
2, power parameters: air pressure, power pressure.
Precautions for valve replacement
If the valve is to be replaced, the following size parameters should be provided to avoid the valve can not be installed, or installed, or space is not enough due to the inconsistency of valve manufacturers, or different standards used, or different valve structure.
As the auxiliary equipment of waste heat power generation system of cement kiln, the valve selection and installation of high temperature flue valve are very important for the safe, economical and efficient operation of waste heat power generation system, although it is small in quantity and value. The high temperature flue valve of waste heat power generation system of cement kiln is different from that of general thermal power plant. There are no problems of high temperature deformation and dust wear of broad plate in thermal power plant. Generally using Q235 steel plate welding, and the thickness is very thin, mostly below 6mm. If this valve is also used in the waste heat power generation system, it is bound to cause wide plate deformation, stuck, bypass leakage rate is large, waste a lot of exhaust gas resources at the same time, the regulation performance is poor. SP furnace bypass valve every
As the auxiliary equipment of waste heat power generation system of cement kiln, high temperature flue valve is very important to the safe, economical and efficient operation of waste heat power generation system, although it is small in quantity and value. The high temperature flue valve of waste heat power generation system of cement kiln is different from that of general thermal power plant. There are no problems of high temperature deformation and dust wear of broad plate in thermal power plant. Generally using Q235 steel plate welding, and the thickness is very thin, mostly below 6mm. If this valve is also used in the waste heat power generation system, it is bound to cause wide plate deformation, stuck, bypass leakage rate is large, waste a lot of exhaust gas resources at the same time, the regulation performance is poor. SP furnace bypass valve for every 1% air leakage, electricity output decreased by 0.6%, so it must be strictly controlled, the design requirements of bypass wide air leakage rate of 1%, relatively large should not exceed 1.5%, but the actual situation is far greater than 1.5%, some even up to 5%. The increase of the leakage rate of AQC furnace bypass valve will also reduce the quality of flue gas.
With the increasingly fierce competition in the supply market of cement kiln waste heat power generation valve, as a non-standard product, the quality of high temperature flue valve products is uneven, and some will deliberately thin the thickness of the broad body and broad plate. Even some broad shaft is 20 boiler steel, a long time will rust to death. Due to the high installation position, long production cycle and high transportation cost of the exhaust gas valve, the cost of replacing the valve is relatively large, so it should be selected according to the technological arrangement of the valve [1]. Now the author on a number of waste heat generation system valve installation and maintenance experience. A summary of valve selection and installation.
1, high temperature flue valve selection
1.1 the AQC furnace valve
(1) the inlet valve
The inlet valve is set between the outlet and the settlement chamber of the grate cooler. It is required that the valve has good regulating performance and reliable operation to adjust the smoke volume of the outlet of the grate cooler. The waste heat generation is usually carried out at the front of the grate cooler. The design temperature is 300~360℃, and it can reach more than 450℃ when the temperature is relatively high. At the same time, the gas medium of grate cooler contains clinker dust with a concentration not more than 30mg/m3 (standard). The speed is generally 8~15m/s. The scour force on the valve plate is very large. Therefore, the valve plate is required to have good wear resistance at high temperature to improve the service life of the valve.
The valve can be selected round or square according to the actual situation, where the temperature is very unstable, and the thickness of the grate cooler bed directly affects the change of the exhaust gas temperature. According to the user, the temperature here is about 450℃ for a long time, but sometimes about 650℃, and can be maintained for about 2h. Valve plates with design temperature ≤450℃ shall be made of 16Mn or No. 20 boiler steel. Valve plates with design temperature ≥600℃ are made of 304 stainless steel. The two materials of the valve plate at high temperature mechanical properties almost no, not to mention good wear resistance. Through site visits and user feedback, we know that when the temperature does not exceed the design range, the general service life is 1-2 years, if the temperature exceeds the design range, the service life is ** half a year. Therefore, the valve plate must use welding degree tortoiseshell mesh, flexural injection with high temperature structural strength, low temperature creep rate, small thermal expansion, strong resistance to chemical erosion, thermal shock resistance and other advantages of flexural injection material, after high temperature baking treatment has strong high temperature resistance and wear resistance, prolong the service life. Heat radiation protection can be achieved by lengthening the yama shaft and welding a thin steel plate between the actuator and the valve connecting rod.
Valve selection:
Structure form: louver type;
Connection form: butt welding, flange;
Leakage rate: 1.5%~2%;
Suitable medium pressure: 0.1MPa;
Body material: No. 20 boiler steel lining heat insulation material and high temperature and wear resistance torsion injection material;
Valve plate quality: No. 20 boiler steel lining high temperature and wear resistant castable when ≤450℃, 304 stainless steel lining high temperature and wear resistant flexible injection material when ≥600℃;
Yan shaft material: 2crl3, 304 stainless steel.
The thickness of the castable should be indicated to the valve manufacturer if the pipe is lined with flexible filling material. In order to avoid the valve installed after the valve plate hit the pipe torsion injection material and can not be opened. The body OF the VALVE shall be coated with the same thickness of insulation and abrasion resistant flex material as the pipe. The advantage of this is that the flow is not turbulent. Avoid greater scour of body and disc by exhaust gas. The thermal insulation layer and the wear-resistant flexure feed reduce the heating temperature of the valve body.
(2) Bypass valve and cold air valve
The bypass valve is located between the tail of the grate cooler and the electrostatic precipitator, and the cold air valve is located in front of the settling chamber for cold air. The residual air temperature of the kiln head fluctuates greatly (180~500℃), the fluctuation period is short, and the bypass regulating valve operates frequently. When the steam production of the kiln head is too large, the temperature of the superheated steam drops, and the bypass regulating Yan is opened to reduce the smoke volume of the boiler in the kiln head. Ensure system stability. Although the temperature of AOC furnace bypass exhaust gas is not high, the leakage rate of valve plate increases after it is scour and worn by clinker dust. In severe cases, the valve plate will fall off, resulting in serious air leakage in the system, resulting in the reduction of evaporation of AOC furnace. When the temperature of the imported smoke is too high, the cold air is added to the settling chamber through the cold air valve. The valve will not be worn out, but the leakage rate is large, which will reduce the quality of the flue gas. Therefore, these two valves require a good seal.
Structure form: single plate, louver type;
Connection form: butt welding, flange;
Leakage rate: single plate 1%, shutter type 1.5%~2%;
Suitable medium pressure: 0.1mpa;
Service temperature: ≤450℃;
Body material: No. 20 boiler steel;
Valve plate quality: 16Mn;
Valve shaft material: 20Crl3.
It is suggested to use single plate valve plate (the shutter type leakage rate is high), and improve the processing accuracy, the leakage rate is controlled within 1%, the bypass valve should strengthen the wear resistance and corrosion resistance, reduce the bypass air leakage volume when the boiler is running.
(3) the outlet valve
The outlet valve is located between the furnace and the electrostatic precipitator, where the exhaust gas temperature is generally below 360℃, the temperature fluctuation is small, the dust wear is weak, and the valve opening and closing action is less. Under normal circumstances, it is in the open state, when the AQC furnace maintenance, the valve is closed. The valve requires good sealing performance when closed to ensure boiler maintenance and personnel safety.
Valve form: insert plate;
Connection form: butt welding, flange;
Leakage rate: ≤0.5%;
Suitable medium pressure: 0.1Mpa;
Service temperature: 330~450℃;
Body material: No. 20 boiler steel;
Valve plate quality: 16Mn:
Valve shaft material: 20Crl3.
The valve is designed as a plug valve structure, the transmission device using sprocket type, to avoid the valve due to ash accumulation caused by the valve opening and closing valve plate deformation, stem bending or burn out electric actuator failure. It should be noted that a set of manual plug valve and rigid impeller feeder should be set between the settling chamber and the zipper machine to avoid the large amount of dust accumulated during the boiler’s stop operation. Here the temperature is relatively high up to 450℃, so the impeller feeder valve body and motor connection mode is connected by coupling, in order to prevent the bin from falling into the foreign body stuck in the unloader impeller. In the burn motor, the dry overload protection device is used to replace the safety pin in the product. At the same time, the shell above the impeller is equipped with inspection holes, the valve shaft is lengthened, the bearing is external, and the refueling hole is added, so as to reduce the fault caused by stuck materials and high temperature.
(4) superheater valve
The superheater valve is generally set between the front end of the grate cooler and the superheater, where the exhaust gas temperature is generally 500~650℃, and the dust content is 30mg/m3(standard). At present, the design department adds less superheater design.
The general design of the valve is louvered, the valve plate is 304 stainless steel. According to the users, the temperature here is mostly maintained at 650℃, and in many cases, it can reach 900℃. Because the valve is subjected to flue gas temperature, corrosion and erosion is particularly serious. Very short service life. Therefore, the valve body should be poured with heat insulation material and castable of the same thickness as the pipeline to ensure that the air flow is not turbulent. The quality of the valve plate is relatively low, and the 304 double-sided welding tortoise shell mesh should be used to cast the high temperature and wear resistance castable to ensure the regulating performance of the valve and the normal operation of the linker production line.
Valve form: louver type;
Connection form: butt welding, flange;
Leakage rate: 1.5%~2%;
Suitable medium pressure: 0.1MPa;
Service temperature: 450~650℃;
Body material: No. 20 boiler steel lining heat insulation material and high temperature and wear resistant castable;
Valve plate: 304 stainless steel lined with high temperature and wear resistant castable;
Fujian shaft material: 304 stainless steel.
Post time: Oct-09-2022
