Steam is closely related to us. From the development and construction of the country to the processing and making of our breakfast, they are all inseparable from the steam generated by steam boilers. Steam boilers bring us a lot of convenience. Here, here, CN Boiler has many years of experience --work experience. Let’s briefly analyze the knowledge of steam boilers so that relevant people can have a certain understanding and knowledge of boilers and have a new understanding of life.
Topics
3. Steam Boiler Control System
6. Common Problems Analysis of Steam Boilers
6.1 Higher Steam Pressure is Better?
6.2 What Causes Pressure Changes in Steam Boilers?
6.3 What are the Dangers of Boiler Overpressure?
1. What is The Steam Boiler
A steam boiler is a thermal equipment that uses the heat energy released after fuel combustion or the waste heat from industrial production to transfer heat to the water in the container, so that the water reaches a certain pressure of steam. It is a complete body composed of "pot" (that is, the water pressure part of the boiler body), "furnace" (that is, the combustion equipment part), accessory instruments and auxiliary equipment. The boiler is carried out simultaneously in the two parts of the "pot" and the "furnace", and after the water enters the boiler, the absorbed heat is transferred to the water on the heating surface of the boiler in the steam system, so that the water is heated into steam at a certain temperature and pressure, which is led out steam to supply workshops. In the combustion equipment part, fuel combustion continuously releases heat, and the high-temperature flue gas generated by combustion transmits heat to the heating surface of the boiler through the propagation of heat, and the temperature itself gradually decreases, and finally is discharged out by chimney.
Steam boilers are special equipment, and their design, production, delivery, and installation must be subject to the supervision of the national technical supervision department. Users need to obtain a boiler usage certificate to operate the boiler. Different from normal pressure boilers, steam boilers must have boiler procedures when leaving the factory. Boiler procedures include boiler body diagrams, installation diagrams, instrument valve diagrams, piping diagrams and inspection certificates, etc.
2. How does Steam Boiler Work
A steam boiler is an energy conversion device that uses the heat energy released by fuel combustion to heat water into steam with certain parameters. The steam boiler is not an independent device, but a complete set of boiler system. The fuel is charged and ignited in the furnace to generate flame and high-temperature flue gas, and the heat is continuously transferred to the water in the pot through the flame and high-temperature flue gas, and the water in the pot is continuously flow circulation, heat absorption and vaporization to generate steam. A good boiler will plan a multi-bend flue gas flow, which is to allow the high-temperature gas after combustion to extend its journey in the furnace body, which can improve the heat conversion rate.
Boiler control system is a collection of boiler electrical control components,a center for collecting and processing boiler operating signals,and an operation platform for sending execution instructions to each execution unit of the boiler.
Core Control Mode: PLC control, PLC+PC control, DCS control
The control system of the industrial steam boiler provides the control of boiler water level,pressure, burning,safety protection and so on.
Control principle: Through the real-time data collection,monitoring and processing of boiler water level, pressure, flue temperature and burning, the purpose of intelligent and safe operation is achieved.
★ Water level Protection
The steam boiler is equipped with two water pumps, running and standby.
The boiler is equipped with one or two plate water level gauges, which should be compared with each other frequently. If the indications are inconsistent, they must be corrected immediately. The water level gauge should be flushed every shift to determine its true water level. It is also equipped with an electrode point water level balance cylinder, which can accurately collect water level signals to issue alarms or control the water supply pump.
★ Temperature Protection
Temperature protection is an important procedure in the safe operation of the boiler. It is particularly important for the regulation and protection of the steam boiler temperature. At the same time, it achieves the regulation and protection function when the boiler is over-temperature. The commonly used temperature protection device for boilers is temperature sensor control.
★ Self-locking Protection When Power Fails
In the event of a sudden power outage, the boiler will immediately shut down and self-lock. If the current is restored, it will start at any time. It must be reset to release the self-lock before it can be re-ignited.
It adopts color and monochrome touch screen control systems, and the operation process is fully automated. It has safety protection systems such as automatic water replenishment, water shortage, over-temperature, over-pressure, automatic power-off and alarm, and leakage protection.
★ Pressure Protection--Steam Pressure Protection
When the boiler pressure exceeds the rated value, chain protection is required: the method is to shut down the boiler and the combustion system stops working; to ensure the safety of the boiler.
The First Protection: High Pressure Alarm-pressure Transmitter
Pressure transmitters control steam pressure. They convert pressure signals into electrical signals and transmit high and low pressure signals to electrical switches for automatic control or interlock protection of external circuits.
Commonly used pressure transmitters can realize the start and stop of combustion status, overpressure alarm, and control the combustion ratio signal.
The Second Protection: if overpressure, the furnace will shut down - pressure controller
Once the steam continues to be over-pressured, the controller will trip, the boiler will shut down, and the system will automatically interlock. It requires thermal engineering to troubleshoot and then restart.
The Third Protection: Exhaust Steam Pressure Relief-safety Valve
The safety valve is the last line of defense in boiler protection. When the boiler pressure exceeds the limit, the safety valve will exhaust steam and release pressure according to the set pressure designed by the safety valve to ensure the safety of the boiler room and staff.
4. Steam Boiler Types
There are many types of steam boilers, which can be divided according to different types as follows:
Application: industry steam boiler, power station steam boiler
Capacity: small steam boiler, medium steam boiler, large steam boiler
Working pressure: low pressure steam boiler, medium pressure steam boiler, high pressure steam boiler
Combustion chamber: internal combustion steam boiler, external combustion steam boiler
Boiler drum arranged type: vertical steam boiler, horizontal steam boiler
Boiler body form: fire tube steam boiler, water tube steam boiler, water fire tube steam boiler
Installation method: integrated steam boiler, bulk steam boiler
Material: steel steam boiler, cast iron steam boiler, aluminum steam boiler
Furnace structure: double return steam boiler, triple return steam boiler
Fuel category: oil fired steam boiler, gas fired steam boiler, biomass steam boiler, coal fired steam boiler, electric steam boiler, waste heat steam boiler
When we choose steam boiler products, we will choose according to the fuel type. We will briefly analyze the steam boiler products of different fuel types.
Gas steam boiler is a steam boiler that burns natural gas, biogas, liquefied petroleum gas, gas, etc., which is the mainstream product in the current boiler products and the product we sell the most. It has one drum steam boiler and double drums steam boiler. The gas steam boiler main has WNS series and SZS series products.
Example: SZS10-1.6-Q=SZS series steam boiler, Rated steam capacity 10t/h, rated working pressure 1.6Mpa(16bar), Fuel is natural gas, biogas, liquefied petroleum gas, and so on.
Oil fired steam boiler is oil-fired steam boiler is a boiler product that burns diesel or heavy oil, and its structure is similar to that of gas-fired steam boiler. It also has one drum steam boiler and double drums steam boiler. The oil fired steam boiler main has WNS series and SZS series products.
Example:WNS8-1.6-Y=WNS series oil fired steam boiler, Rated steam capacity 8t/h, rated working pressure 1.6Mpa(16bar), Fuel is diesel, heavy oil.
Coal steam boiler is the boiler that burns coal such as, it belongs to the traditional boiler products, the price is cheap, loved by customers, he has water hot pot boiler, water tube boiler. The coal steam boiler main has DZL series, SZS series and SHX series products. Different coals have different combustion characteristics, we will design different boiler bodies according to the characteristics of coal, in order to achieve the purpose of full combustion of fuel
Example: SHX10-1.6-AII=SHX series circulating fluidied bed steam boiler, Rated steam capacity 10t/h, rated working pressure 1.6Mpa(16bar),Fuel AII: AII means Class II bituminous coal.
(Remark: WII:Class II anthracite, WIII:Class III anthracite, AI:Class I bituminous coal, AII:Class II bituminous coal, AIII:Class III bituminous coal, H:lignite, P:lean coal)
Biomass steam boiler is a steam boiler product burning biomass, because the fuel of biomass steam is made of straw, wood chips, firewood, rice husks, palm and other agricultural waste processing, so its fuel cost is low, the operating cost is low, received a lot of customers favor, it is currently all boilers in the operating cost of the boiler product. The biomass steam boiler main has DZL series and SZS series.
Example:SZL10-1.6-SCIII=SZL series steam boiler,Rated steam capacity 10t/h, rated working pressure 1.6Mpa(16bar), Fuel is biomass particles, rice rusk, palm shell, and wood chips etc.
The electric steam boiler is a boiler product fueled by electricity. Because it burns electricity, it has the advantages of clean environmental protection, ultra-high thermal efficiency, and safe and reliable performance. But the steam boiler also has the corresponding disadvantages, that is, the operation cost is too high. It is usually named LDR/WDR.
Example: LDR72-0.7=LDR series electricity steam boiler, electricity power 72 kw, rated working pressure 0.7Mpa(7bar), Fuel is electricity
Waste heat boiler is the boilers which use the waste heat in the waste gas, waste material or waste liquid in various industrial processes and the heat generated by the combustion of combustible substances to heat the water to a certain temperature. The waste heat boiler can produce steam through waste heat recovery to supply other production processes. Since the waste heat boiler greatly improves the utilization rate of the heat released by fuel combustion, so the waste heat boilers are very energy-saving.
5. Steam Boiler Application
Steam boilers are used in many industries, such as food industry, beverages industry, wineries industry, feed industry, paper industry, textile industry, clothing industry, oil refining industry, chemical industry, petroleum industry, packaging industry, central heating, hotels, mining industry, construction industry, and so on.
The following takes the printing and dyeing industry, food processing industry, feed industry, and pharmaceutical industry as examples to briefly explain the role of steam boilers in those industries.
Printing and Dyeing Industry: The main process is divided into 3 steps: pre-treatment, dyeing and printing, and finishing. The main processes include singeing, desizing, scouring, bleaching, mercerizing, setting, drying and dyeing. Usually, when equipment conditions permit, steam boilers are generally used to supply steam in the drying and sizing links, while heat transfer oil boilers are used to provide heat sources in the dyeing links. Due to the characteristics of high pollution and high consumption in the printing and dyeing industry, considering the requirements of environmental protection, energy-saving and high-efficiency gas-fired boilers are widely used.
Food Processing Industry: It is mainly used for distillation, disinfection, drying, curing and other processes in food processing, and high-temperature steam is used for high-temperature cooking, drying and disinfection of food. Therefore, steam boilers are used most frequently, and steam is mainly transported through pipelines, requiring constant steam temperature and pressure, and even the quality of steam determines the quality of food from the factory. Some food factories also use hot water boilers for central heating of their workshops and office buildings, or special processing of certain foods.
Feed Processing Industry: During the processing of the feed mill, the boiler will work together with the twin-shaft paddle mixer, pulverizer, vertical twin-shaft pulverizer, granulator, conveyor, packaging machine, etc. During granulation and tempering, steam is needed to make the temperature of the material reach 80-85 degrees and the moisture content reach about 17%. Due to the large fuel consumption, the application frequency of coal-fired steam boilers is very high. However, with the increasingly stringent environmental protection supervision, in order to meet environmental protection standards, more and more gas-fired boilers are used.
Pharmaceutical Industry: A large amount of steam is required for high-temperature sterilization of raw materials and equipment, and heating is provided in the drying and cooling, tableting and granulating links. The requirements for steam are relatively high, and its proportion of energy consumption is also relatively large. In the past, coal-fired steam boilers and biomass boilers were used frequently, but with the emphasis on environmental protection in various countries, it has become a difficult problem for many pharmaceutical companies to reduce energy consumption as much as possible while meeting production requirements. Pharmaceutical companies choose our energy-efficient gas boilers.
6. Common Problems Analysis of Steam Boilers
Higher Steam Pressure is Better?
The selection of boiler steam pressure mainly depends on the user's needs. Low steam pressure is beneficial to the safety of pressure-bearing parts and has low energy consumption. However, the quality of steam is poor, the heat enthalpy is low, and the humidity is high. It is even difficult to meet the needs of disinfection, sterilization, culture, heating, and power generation. If the steam pressure is too high, the energy consumption will be high. The corresponding steam equipment, piping systems and valves will also be under high pressure, and the maintenance requirements will be higher. The heat dissipation and leakage losses during the steam production and transportation process will also be large. At the same time, the salt content carried by high-pressure steam increases as the steam pressure increases. These salts increase the possibility of scaling, overheating, foaming, blockage, and even pipe explosion on heating surfaces such as water wall tubes, smoke tubes, and drums. The entry of steam salt into the steam turbine will reduce the turbine flow area, reduce the internal efficiency, and seriously affect the heat transfer.
Therefore, the boiler must operate according to the specified working steam pressure. Generally, the allowed steam pressure fluctuation value is 0.05~0.15MPa.
What Can Cause Pressure Changes In Steam Boiler?
External Disturbance: Changes in steam pressure caused by external load changes are called external disturbances, or "external disturbances" for short. When the external load increases, the steam consumption of the unit increases, and the boiler has not yet had time to adjust to the new working conditions. The boiler evaporation capacity will be less than the external demand for steam, the material balance relationship is broken, and the steam pressure drops.
Internal Disturbance: Changes in steam pressure caused by changes in the working conditions of the boiler itself are called internal disturbances, referred to as "internal disturbances". The demand for steam from the outside world does not change during operation, but due to changes in boiler combustion conditions (such as unstable combustion or changes in fuel volume and air volume) and changes in the working conditions in the boiler (such as heat transfer conditions), the steam production changes in the evaporation area, the material balance relationship between the boiler evaporation capacity and steam demand capacity is destroyed, causing the steam pressure to change.
What Are The Dangers of Boiler Overpressure?
Metal Materials have their own specific yield strength at a specific temperature. Over-pressure operation will cause thermal fatigue of metal materials. Operation under fatigue limit conditions will cause a decrease in yield strength. Breaking through the yield limit will cause rapid creep until bursting.
The strength of metallic materials can be compensated under certain conditions by increasing the wall thickness of the metal. The increase in wall thickness will increase the temperature difference between the inner and outer walls and reduce the heat transfer rate. The wall temperature difference will cause the thermal stress of the metal material to increase and accumulate.
There is a rated pressure when the boiler is designed, which is also the maximum allowable pressure during boiler operation. If it is normal, this pressure is controlled by the safety valve of the boiler. Ultra-high phenomena should not occur. This phenomenon is also not allowed. If it occurs, that is, the boiler's design parameters are exceeded, which will affect the service life of the boiler. The steam pressure is too high and the mechanical stress is too large, which will endanger the safety of the boiler, furnace and steam pipes. When the safety door is opened, a large amount of exhaust steam will be lost.In addition, if the safety door is often opened, it will also cause wear or dirt to be deposited on the valve. It is easy to cause loose closing of the seat back, resulting in regular loss of steam leakage. Sometimes the furnace even needs to be shut down for maintenance. If it is too high, it can easily cause The heated pipes swell, causing pipe burst accidents. High-parameter operation improves certain economic benefits as far as boilers are concerned. But the consequences are also huge!
7. Conclusion
We hope that this short article has answered some of your questions related to steam boilers. However, we believe in the old adage, “The more you learn, the less you know.” In other words, we realize that this article may not have answered all your questions and may have actually generated new ones. Please do not hesitate to contact us or our representatives to obtain any additional information you may require.
Thank you for reviewing the article and considering CN BOILER as a potential partner in your next energy project.
If you want to learn about the detailed parameters and prices of steam boilers, please contact us: at +0086 132-9831-1147.
