In the industrial and commercial fields, the efficient operation and safety of boilers are crucial. Any slight negligence may cause serious production accidents and huge economic losses. And boiler discharge, as a key maintenance measure, plays an indispensable role in the stable operation of boilers. In this paper, we will discuss the correct process, type and importance of boiler discharge to help the relevant personnel to fully understand this important operation.
Definition
Boiler sewage, in simple terms, is the process of discharging some water from the boiler system. Its main purpose is to remove impurities, suspended solids, and sludge from the water. We all know that the water into the boiler, even after pretreatment, it is difficult to completely avoid the mixing of impurities. And these impurities will gradually accumulate during the operation of the boiler. At the same time, the quality of the water has a direct correlation with the amount of discharge. The better the water quality, the less water needs to be discharged, which is a basic correspondence.
Role in boiler maintenance
From the maintenance point of view, boiler discharge is mainly used to control parameters such as total dissolved solids (TDS) and total suspended solids (TSS) in the water. When these solids accumulate too much in the boiler water, it will have many adverse effects on the operation of the boiler. Through regular sewage discharge, these parameters can be effectively controlled within a reasonable range, thereby extending the service life of the boiler. In addition, since water is lost through evaporation during boiler operation, it is necessary to replenish fresh make-up water. In this process, the sewage operation is particularly important, it can ensure the balance of the water quality of the entire system.
Surface skimming
This type of sewage is from the top of the boiler water level slowly and continuously remove part of the water. In terms of operation, it can either be manually adjusted needle valve to precisely control the flow of water from the surface discharge, or it can be realized with the help of automated equipment. The automated system usually consists of a conductivity sensor, a motorized valve, and a controller.
The sensor monitors the quality of the boiler water in real time, and once the water quality parameters deviate from the set range, the controller issues a command to open the surface drain valve to maintain the set value of conductivity. This type of discharge is very effective in dealing with impurities, and it provides good control of cycling the concentration of impurities in the water with as little loss of boiler water as possible. In determining the appropriate boiler water quality target, we can refer to the literature provided by the boiler manufacturer.
Bottom drain
Bottom discharge is the most commonly used type of discharge because it is effective in preventing the accumulation of dissolved solids. At the bottom of the boiler, two valves are connected, one is a slow opening gate valve and the other is a fast opening knife gate valve. When draining the bottom, first make sure that both valves are fully closed. Then, open the knife gate valve first and then open the gate valve fully. In this way, the discharge operation can begin. As for the length of time for discharging, it is usually necessary to consult a water treatment professional who will give reasonable advice according to the specific situation.
During the draining process, it is necessary to keep a close eye on the water level changes in the glass tube of the water level gauge, as it may sometimes be necessary to shorten the draining cycle in order to ensure that the proper water level is maintained in the boiler. After completing a drain, close the gate valve, then repeat the operation of opening and closing the gate valve again, three times in total. The purpose of this is to cause the water inside the boiler to fluctuate by repeating the operation, thus pushing the sludge at the bottom towards the drain.
Finally, close the gate valve and then the knife gate valve. After completing the drain operation, it is also necessary to open the gate valve again to empty the water in the piping between the gate valve and the knife gate valve, and then close the gate valve after it has been emptied. When the valve is cooled, check whether the valve is closed tightly to ensure that there is no leakage.
Water column sewage
Water column sewage is mainly to control the accumulation of sludge in the water level control system and the glass tube of the water level meter. In this process, it is necessary to clean the water level gauge glass tube, water column, and the related sewage piping system and valves to remove the impurities. This operation ensures that the operator has a clear view of the water level in the boiler. In the case of the float-type low water cut-off device, it has a bowl-shaped assembly in which sludge can build up if it is not drained on a regular basis, thus affecting the normal movement of the float assembly.
Other related systems and components
Effluent Heat Recovery System: This system is designed to recover energy that would otherwise be wasted. It utilizes the heat in the discharged effluent to preheat the feedwater before it enters the boiler. In this way, energy that would otherwise be wasted is recaptured, reducing costs and improving the overall efficiency of the boiler room.
Drain separator: this is a specially designed vessel that has two main important functions. On the one hand, it is able to reduce the high-pressure discharge from the boiler to near-atmospheric pressure by means of steam flashing; on the other hand, it is equipped with an aftercooler that cools the discharge before it enters the drain line.
Drain Tank: The drain tank is also used to reduce the high pressure discharge to atmospheric pressure. Unlike the drain separator, it does not immediately cool the discharge and discharge it into the sewer, but first collects and stores the discharged water and allows it to cool naturally before discharging it.
The bottom of the sewage process
Valve opening order: as mentioned earlier, the two valves on the bottom sewage piping, the operation must be strictly in order. First close the two valves, and then first open the knife gate valve, then open the gate valve, this order can not be reversed.
Sewage operation: after the valve is opened, start sewage. Discharge time according to the recommendations of the water treatment professionals, while paying close attention to the water level in the glass tube of the water level meter changes, so as to adjust the length of the sewage.
Repeat the procedure: After closing the gate valve, repeat the action of opening and closing the gate valve three times in order to push the sludge to move towards the drain.
Close valves: Close the gate valve and then the knife gate valve to complete the basic drain shut-off action.
Final Drainage and Inspection: Open the gate valve again and close it after emptying the water in the pipe between the two valves. Wait for the valve to cool down, check whether the closure is tight to prevent leakage.
Surface skimming sewage flow
Automated operation part: In most cases, the surface skimming sewage from the water treatment professionals to set the rate to achieve automated operation.
Conductivity Measurement: The operator needs to use an accurately calibrated conductivity meter to measure the conductivity of the boiler water to determine the amount of sewage required.
Water transfer operation: Based on the measurement results of the conductivity meter, boiler water is introduced into the skimmer pipe through a needle valve or throttle valve to maintain the boiler water conductivity within the specified range.
Additional maintenance points: the safety valve, level switch and water level meter glass tube must be drained every week to ensure that these devices can work properly when needed.
Preventing the accumulation of solids
Although we have taken various measures in the process of water replenishment and feedwater pretreatment to try to prevent hardness and other solid impurities into the boiler, but inevitably there will be some impurities mixed into it. Boiler discharge, however, is used to maintain a predetermined concentration of hardness and solids in the boiler water by discharging a small amount of higher hardness, higher solids content water and replenishing lower hardness, lower solids content make-up water.
Cost and performance advantages
Proper discharge operation keeps the boiler running optimally, thus maximizing its performance. It also helps to reduce boiler maintenance and repair costs. It is important to understand that maintaining low hardness and low dissolved solids in the boiler is costly because every gallon of effluent discharged has already been heated and treated. Therefore, finding the right amount and frequency of discharge is important for every boiler application.
Factors affecting discharge
The discharge volume and discharge frequency are not fixed, but are affected by a number of factors. For example, the type of boiler varies and so will its discharge requirements; the level of operating pressure will also have an effect on discharge; the way the water is treated and the amount and quality of make-up water will, to a certain extent, determine the discharge requirements of the boiler.
Problems with heating surface insulation
When excessive solids and sludge accumulate on the heating surfaces on the water side of the boiler, a layer of insulation-like material can form. This causes the metal to be unable to dissipate heat efficiently, and overheating occurs as a result. If this situation continues to develop, it may eventually lead to failure of the boiler's pressure vessel.
Problems with steam carrying water
High concentrations of hard and dissolved solids can also cause boiler water to be carried out with the steam, a phenomenon known as steam carryover. Steam carryover can cause water hammer, which can result in serious damage to piping and equipment.
Low water level
The accumulation of solids may also cause low water level. Because these solids will occupy a certain space, affecting the normal measurement and control of the water level.
Solids circulation problems in steam boilers
In a steam boiler, solids remain in the water as the boiler water is converted to steam. Unless 100% of the condensate can be returned to the boiler, the hardness and concentration of dissolved solids in the water will continue to cycle up as the boiler is replenished with new make-up water. In hot water systems, if make-up water is not normally used, then the concentration of solids in the water will remain relatively stable, and there is no need to carry out sewage operations.
Requirements for operating conditions
Boiler discharge operation, make sure that the boiler is at a high water level and low load condition. This can maximize the safety and effectiveness of the sewage process, to avoid the water level is too low or load is too high and cause other problems.
Single boiler operation
In the discharge operation, must ensure that only one boiler in the discharge, is strictly prohibited at the same time on two or three boilers discharge operation. This is to prevent excessive fluctuations in the pressure and water level of the entire system due to simultaneous discharge, affecting the normal operation of the boiler.
Valve operation specification
When discharging sewage, the valve must be opened slowly, and rapid opening or closing of the valve is strictly prohibited. Rapid operation of the valve may lead to excessive water flow impact, causing damage to the pipeline and valve, and may also trigger the water hammer phenomenon, jeopardizing the safety of the entire system. In addition, when opening the sewage valve, special attention should be paid to the opening sequence of the valve, and it is strictly prohibited to use the sewage valve in front of the furnace to control the sewage process.
Comprehensive sewage principle
In the process of sewage disposal operations, both sides of the boiler and the back side of the sewage, not just one side of the operation. This will ensure that the impurities in all parts of the boiler can be effectively discharged to ensure the comprehensiveness and effectiveness of the discharge.
Emergency response measures
In the operation process, if you encounter special circumstances that can not be dealt with, you should promptly report to your superiors, or immediately carry out emergency furnace shutdown operations. It is important not to ignore these abnormalities so as not to cause more serious accidents.
Boiler sewage seems simple, but it contains many complex links and important knowledge. The correct sewage process, the appropriate type of sewage selection and strict compliance with sewage notes, to protect the efficient operation of the boiler, extend the service life of the boiler and ensure production safety are of great significance. Relevant operators must carefully study and strictly implement these requirements, and consult professionals when encountering problems to ensure that the boiler is always in the best operating condition.
