Regular boiler blowdown control
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The control of water quality in boilers and steam quality has always been a challenge for medium-pressure boilers, especially those that supply steam as a power source for turbines. Boiler design generally includes fixed drainage and continuous drainage. Design requirements for the fixed pipe diameter cannot be found in various sources; is it DN50 or DN40? Should it be turned on fully or halfway? How long should the waste discharge last? Some companies install flow-limiting orifice plates before and after the fixed-discharge valves, but these orifice plates restrict the flow rate, which results in an ineffective fixed-discharge function. I was wondering if David knows of any relevant regulations or books that could be referenced
During the regular blowdown of boilers, few operations follow a time interval of 20–30 seconds; generally, it is between 5 and 7 seconds. If the blowdown takes too long, the boiler is prone to running out of water or experiencing a drop in pressure. However, to compensate for the poor effluent discharge performance resulting from a short discharge time, the secondary discharge method is used; that is, after one discharge operation, once the water level and pressure have stabilized, another discharge operation is carried out.
How should the quantity and quality of regular wastewater discharge be determined? The main purpose of regular blowdown is to remove the scale at the bottom of the boiler, but there is no way to determine whether the scale has been removed. There must be some standard for regular blowdown, right?
The diameter of the pipes used for regular drainage from boilers is generally not large; if it is large, it is not possible to maintain the liquid level in the boiler’s drum, and heat loss also increases. Slag generally settles at the bottom; regular discharge can only remove a large amount of impurities in the first few seconds after it is activated, with most of the flow being furnace water thereafter. The usual approach is to turn it on for a few seconds and then turn it off, wait for it to stabilize, and then turn it on again for a few seconds; this results in better removal of water residues compared to leaving it on for 20-30 seconds straight. In fact, each boiler is different, and specific operations must be carried out based on experience, with the goal of removing most of the water sludge without affecting the liquid level in the steam drum.
The sum of the quantities. This involves monitoring the total amount of pollutants emitted from a specific monitoring site over a certain period of time. Specifically, it is necessary to continuously remove from the drum the portion of boiler water whose salt content increases due to water evaporation, in order to maintain the required quality of the steam. At the same time, regular blowdown must be taken from the part of the boiler water with the highest salt content, in order to remove impurities such as sediment and rust from the water, and prevent these impurities from causing scaling and blockages in the water wall tubes. Regular sewage discharge should be taken from the lowest point of the circulation loop, that is, the area where the most sediment accumulates, on a intermittent basis. Determination of quality: The quality of regular waste discharge is primarily related to the impact of the discharging entity on the environment, including but not limited to gaseous pollutants, aquatic pollutants, and solid waste. When designing a self-monitoring plan, these elements should be taken into full consideration to ensure that the entire monitoring process covers all elements and indicators. Furthermore, for new chemicals or pollutants that have not yet been included in standards or lists of pollutants to be controlled, monitoring should also be carried out if it is determined that their release has an impact on public health or environmental quality, in order to prevent risks.2 Through the above methods, it is possible to effectively determine the quantity and quality of waste discharged regularly, ensure that the environmental protection measures taken by the waste-discharging entities comply with relevant regulatory requirements, and at the same time provide a scientific basis for environmental protection.