What is the drainage index of boiler drum water?

Simply put, just ensure the quality of the boiler water.

Repost 1. The concept of boiler blowdown: 1. In order to control the water quality of the boiler water to meet the prescribed standards and keep the impurities in the boiler water within a certain limit, it is necessary to continuously remove the boiler water containing large amounts of salt and alkali and the deposited slag, sludge and loose sediment from the boiler. This process is boiler blowdown. 2. Sewage discharge method: Boiler blowdown is divided into two types: continuous blowdown and regular blowdown. Continuous blowdown, also known as surface blowdown, requires continuous discharge of part of the boiler water from the part with the highest salinity and alkali concentration in the boiler water to reduce the salt, alkali, silicic acid and suspended slag content in the boiler water. Therefore, the continuous blowdown pipe is located at 80~100mm below the normal water level. Regular blowdown mainly removes sediments such as water slag and mud in the furnace, so the blowdown port is mostly set at the lower part of the drum and the bottom of the header. The periodic blowdown operation is short-lived and should be performed when the boiler is in a high water level, low load or pressure fire state. On small boilers, only periodic blowdown is usually installed. 2. Calculation of boiler blowdown: The size of the boiler blowdown is directly related to the quality of the feed water. The greater the alkalinity and salt content of the feed water, the greater the sewage blowdown required by the boiler. 1. Calculation of pollution discharge rate: The indicator of boiler blowdown is expressed by the blowdown rate, which is the percentage of the discharged water volume (Q pollution) to the boiler evaporation volume (Q steam). Expressed as follows: K= Q dirt/Q steam × 100 % When the boiler water quality is stable, according to the relationship between mass balance, the amount of a certain substance brought into the furnace with the feed water is equal to the sum of the amount drained away by the sewage and the amount taken away by the saturated steam. Then (Q pollution + Q steam) × S feed = Q steam Then K = Q pollution/Q steam = (S supply - S steam) / (S pollution - S supply) × 100 % 2. Pay attention to the following three points when calculating the pollution discharge rate: (1) The discharge rate can be calculated based on alkalinity or chloride ions (chloride ions have a relatively fixed proportional relationship with salt content, and chloride ions are usually used instead of salt content). Finally, the larger value is taken as the discharge rate. Generally, the discharge rate of heating boilers should be controlled below 10%. (2) For boilers with larger capacity, the humidity of steam is very small due to the effective steam-water separation device. In this way, the salt content in the saturated steam is much lower than the salt content in the feed water, so the salt content in the steam can be ignored in the calculation of the pollutant discharge rate of this type of boiler, that is, K=Sfeed/(Spollution-Sfeed)×100% (3) For most industrial boilers, especially those with small steam drum volumes, simple steam-water separation devices, and large water content in saturated steam, the steam humidity is usually around 3% (compared with the sewage rate control of 5% to 10%, which is not low). Under these conditions, the salt content in the steam cannot be ignored when calculating the boiler sewage rate. Because K= (S to - S steam) / (S pollution - S to) = CL - to / (CL - pollution - CL - to) - CL - steam / (CL - pollution - CL - to) < CL-feed/(CL-dirty-CL-feed)-CL-steam/CL-dirty where CL-steam/CL-dirty is the steam humidity, CL-dirty = CL-boiler water, that is, the chloride ion content in the wastewater is equal to the chloride ion content in the boiler water, where CL-give, CL-dirty, CL-steam, and CL-boiler water respectively represent the chloride ion content in the feed water, the drained water, the saturated steam, and the boiler water. It can be seen that if the salt content in the steam is ignored, the calculated sewage discharge rate will be too large (the difference is greater than the steam humidity). For every 1% increase in the sewage rate of industrial boilers, fuel consumption increases by 0.3%. This wastes fuel and cannot correctly evaluate the boiler's energy consumption and comprehensive management level. 3. Boiler blowdown device: The blowdown device refers to the short blowdown pipe within the boiler body, the blowdown valve and the blowdown pipe inside the drum, etc. The sewage duct must be of sufficient length and installed horizontally, with one end of the duct sealed. Each boiler should be equipped with an independent sewage pipe. The sewage pipe should have as few elbows as possible to ensure smooth drainage and be connected to a safe location. The connections between the sewage pipe and the drum, header, and sewage valve must be secure and free of corrosion. The drain valve should be a gate valve, sector valve or inclined stop valve. For boilers with a nominal diameter of φ20~65mm and a rated evaporation capacity ≥1t/h or a working pressure ≥0.7Mpa, the sewage pipe should be equipped with two sewage valves in series. During sewage discharge, the sewage valve is subject to the erosion of high-temperature liquid and the wear and tear of dirt. After the sewage discharge is stopped, it will gradually cool to room temperature. In order to improve the blowdown valve's ability to frequently withstand harsh working conditions such as pressure difference (large pressure drop), scale corrosion, wear, vibration, thermal shock, etc., the series-connected blowdown valves have a certain operating sequence. The connection sequence is the drum (or lower header) - valve 1 (slow valve), valve 2 (fast valve). When blowing down the blowdown, open valve 1 first and then valve 2 (valve 2 is subject to the pressure difference and is easily damaged) ； When stopping sewage discharge, first close valve 2, then close valve 1 (valve 2 is subject to pressure difference and is easily damaged). This allows valve 1 to open and close without pressure difference, with good working conditions and long life. During overhaul, focus on repairing or replacing valve 2. Valve 1 is a slow-opening valve. It often uses a slant ball type blowdown valve or a slow-opening gate type blowdown valve, which is an ordinary gate valve, but it must have the ability to resist the alkaline corrosion of furnace water. ； Valve 2 is a quick-opening valve, often using swing gate type or rack gate type valves to meet the action and time requirements of sewage discharge. 4. Recovery and Utilization of Blowdown Heat The blowdown rate of a boiler is generally 3 to 10% of the boiler capacity. In order to recover and utilize the non-negligible heat brought out by this part of the wastewater, regular blowdown and continuous blowdown expanders are usually installed in the boiler room. Separate the steam and water produced after the boiler water is depressurized and use them separately. The steam is generally passed into the atmospheric thermal deaerator for deoxygenation of the feed water, while the sewage is cooled through the heat exchanger to utilize the heat and then safely discharged into the ditch. 5. Summary: Remove impurities, mud, and scale from the boiler water through correct and reasonable sewage discharge, and control the alkalinity and salt content of the boiler water to ensure that the boiler water quality meets * * Standards ensure the cleanliness of the heating surface, meet qualified steam quality requirements, extend the service life of the boiler, make full use of waste heat from wastewater, and achieve energy saving effects. It can be seen that the design, manufacturing, installation and user units must pay attention to the issue of boiler sewage discharge, deeply understand the significance of sewage discharge, grasp the size of the sewage discharge, correctly operate and use the sewage discharge device, and recycle the waste heat of the sewage discharge. This will help ensure that the boiler operates safely, reliably and for a long time under economic conditions, reduce unnecessary losses, and achieve the purpose of saving energy.