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Several common questions about condensing gas boiler

2020-08-15 14:20    page view:

Guide: 1. Why is there a certain height difference between the steam drum and the waste heat boiler? Answer: The water in the condensing gas boiler and the steam drum relies on gravity to circulate. A certain height difference is conducive to the separation of steam and water and helps prevent reverse circulation in the boiler.

  1. Why is there a certain height difference between the steam drum and the waste heat boiler?

Answer: The water in the condensing gas boiler and the steam drum relies on gravity to circulate. A certain height difference is conducive to the separation of steam and water and helps prevent reverse circulation in the boiler.

   2. Why doesn't ammonia water be directly added to the deoxygenation tank?

  Answer: The ammonia water is not directly added to the deoxidation tank, because ammonia water can cause corrosion in the presence of oxygen.

  3. What is the function of the steam drum safety valve? How to set it? What is the constant pressure?

  Answer: The safety valve is an important accessory of the boiler system. It is used to prevent rupture or other damage accidents when the steam pressure in the drum exceeds the limit. When the pressure in the steam drum exceeds the specified value, the safety valve will automatically open to release some steam and reduce the pressure. When the pressure drops to a normal value, it will shut itself down to maintain the normal operation of the boiler. For boilers with an evaporation capacity greater than 0.5t/h, at least two independent safety valves should be installed, one of which is fixed at 1.04 times the normal operating pressure of the boiler, and the other at 1.06 times the normal operating pressure.

4. The purpose of controlling the PH value of condensing boiler water? What is the harm if the PH value is too high or too low?

  Answer: Under the operating conditions of carbon steel, gas boilers have different corrosion rates for boiler water with different pH values. Controlling the pH value of boiler water within a certain range is to prevent acid or alkaline corrosion of the boiler. When the PH value is lower than 8, acid corrosion will occur, and the reaction products are all soluble, and a protective film cannot be formed, which accelerates the corrosion. When the PH value is higher than 10.5, free NaOH may appear, causing alkaline corrosion.

   5. What are the phenomena, causes and treatments of the co-leakage of soda and water in the steam drum?

Answer: The water level in the drum water level gauge vibrates violently when the gas-water condensing boiler is co-piping, and the water level is not clear; the temperature of the superheated steam drops sharply, and water hammer occurs in severe cases; the quality of steam and boiler water deteriorates; the water level alarm sounds intermittently High or low alarm signal.

   The reasons for the co-leafing of steam and water are: the salt content of the boiler water exceeds the prescribed index too much, and the sewage is not discharged in time; the water level is too high, and the steam load of the boiler water increases sharply when the boiler water is at the limit level; the feed water contains too much oil and dosing.

Treatment methods for co-leafing of steam and water: reduce boiler load, that is, reduce steam production; strengthen regular and continuous blowdown, and at the same time strengthen water supply to prevent water shortage caused by low water level; strengthen boiler water analysis, perform blowdown according to the analysis results, and improve the furnace Water quality; the water level should be controlled at 50%±50mm.

   6. What causes the excessive SiO2 in steam? What is its harm?

Answer: The reasons for the excessive SiO2 in the steam are: improper pretreatment of the feed water. When the SiO2 content of the boiler water exceeds 3ppm, the SiO2 in the steam exceeds the standard; the boiler water foams, the steam and water azeotrope or steam entrainment, and the steam drum level is high. Cause SiO2 to exceed the standard. The SiO2 carried in the steam will deposit on the one-way valve, shut-off valve, superheater, steam turbine blades, reformer tube and catalyst of the steam system, which will damage the turbine blades or reduce the turbine output and reduce the heat exchange effect. Catalyst clogging, etc.

  7. What is the three-impulse adjustment of the drum water level?

Answer: In the waste heat operation of a low-nitrogen gas condensing boiler, maintaining a stable drum water level is the most important operation. The drum water level is not only affected by the change in the water supply, but also by the steam production. Therefore, the use of single parameter water level adjustment is not ideal. It is necessary to use a method with a certain difference between steam and water to control the water intake to make the drum water level More stable. This method of controlling the water level of the drum is customarily called three-impulse adjustment. The three-impulse adjustment is actually a cascade adjustment. Drum water level is the main parameter of this regulation system, that is, in this control loop, the output signal of the water level regulator is used as the set value of the cascade regulator, and the difference between the steam flow and the feed water flow after the adder is taken as the series The measured value of the level regulator (secondary parameter). As long as there is a deviation between the measured value and the given value, the cascade regulator outputs a signal to control the change of the inlet water flow.

  8. What should I pay attention to when raising and lowering pressure and temperature of the steam drum?

  Answer: The waste heat boiler in the methanol plant generally belongs to the range of high and medium pressure boilers, and the drum wall is thick. Therefore, when driving (heating, boosting) and stopping (cooling, depressurizing), the most important things to note are the following three:

  (1) The difference between the inlet water temperature and the drum wall temperature should not exceed 50°C;

  (2) The heating rate is not more than 55℃/hr or the pressure rising rate is not more than 1.0Mpa/hr;

   (3) When stopping, use the original boiler water system to circulate the temperature and pressure, and it is not allowed to remove hot water suddenly into cold water.

   There is only one purpose of the above three attentions, which is to prevent the occurrence of excessive stress. Because the steam drum is not only a thick-walled pressure vessel, it is also connected with many water and steam pipelines through many openings. The thermal stress caused by the sharp rise and fall of temperature during operation and shutdown is prone to cracks, which damage the strength of the equipment.


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