Analysis and treatment of high dissolved oxygen in condensate of power plants - Master's thesis - Dissertation

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Cause Analysis and Treatment of High Dissolved Oxygen in Condensate of Power Plant

The high dissolved oxygen content of the condensate in the power plant will lead to changes in conductivity and vacuum system, and corrosion of equipment in the condensate system, especially for natural gas generator sets. Due to the special nature of the heat cycle of the waste heat boiler, the condensate is directly pressurized by the condensate pump. After entering the low-pressure economizer #1 of the waste heat boiler, most of them are pressurized by the low-pressure recirculating water pump and then enter the low-pressure economizer #2, and then enter the low-pressure steam drum. Undoubtedly, when the dissolved oxygen content of the condensate is high, it is bound to be It adversely affects the safe operation of the above equipment. The author combines his own years of experience to conduct a comprehensive analysis of the long-term high temperature of dissolved oxygen in a power plant, to explore the reasons for its high, and to adopt some treatment methods and measures. It has been proved by practice that very good results have been obtained. The amount of dissolved oxygen in the condensate during operation is less than 10 μg/L, which is far below the power plant control standard. In order to further summarize the experience and learn from each other and exchange with each other, it is summarized as follows:

Cause Analysis

1. Reasons for transformation: The dissolved oxygen content of a power plant has been high since its production. The normal value is ≤30-40μg/L. The dissolved oxygen content of a condensate in a plant has been fluctuating up and down at 80μg/L, exceeding 120μg/L when the unit is shut down. We carefully examined this phenomenon and analyzed the parameters:

(1) Excludes the leakage caused by the condenser, because the internal leakage of the condenser will not cause the dissolved oxygen to increase, other parameters will also change, such as the sodium ion content will increase, the conductivity will change, and the vacuum system will also deterioration.

(2) We have carried out a comprehensive inspection of the condensate system, such as the condenser side steam discharge valve, from the condensate hot water well to all the flanges of the condensate pump, pressure gauge joints, drain valve, inlet water filter cover, etc. There is a leak, and we have also replaced the condensate pump seal packing, etc., which has not changed the dissolved oxygen level.

(3) We further inspect the sealing water of the condensate pump packing and find that the condensate pump is sealed by desalinated water. The sealing water system is as shown in the figure, and there are obvious deficiencies in the design of the sealing water system. High leakage, the condensate is installed in front of the water pump seal ring, a three-way valve is installed, one way is to remove the salt water, one way to enter the water seal ring inside the water pump packing ring, the other way is directly introduced into the pump inlet side, directly Enter the condensate system.

2. The improved method is to transform the original sealed water into two-way water supply. When the two pumps are stopped or started at the same time, the water is dehydrated. When the condensate starts normal operation, the outlet water of the condensate pump is decompressed through the pressure reducing valve. The water supply header is separately supplied to the running pump and the standby pump, and the two water pressure difference and the check valve function are used to automatically switch the two waters without manual operation.

3. The main equipment function of the system: the outlet pressure of the condensate pump is about 3.3Mpa. After the high pressure condensate enters the water seal ring of the stuffing box, the sealing packing will be over-compressed, causing the sealing packing to wear with the pump bushing, and the burning filler will cause leakage. Then wear the bushing and damage the equipment. Set the pressure reducing valve in the system to reduce the pressure of the condensate pump to about 0.8Mpa into the sealed water supply header. The water supply header is to stabilize the sealing water pressure and flow and supply water to both pumps at the same time. Install a check valve on the demineralized water and self-water supply connecting pipe to keep the self-supply pressure higher than the demineralized water pressure by 0.2-0.5Mpa. When the water supply is self-supply, the check valve is closed due to the pressure difference. When the water pump is running, the self-water supply The pressure is 0, the check valve is opened, and the brine is supplied.