During the operation of some types of industrial plants, large volumes of exhaust gases with a very high temperature are emitted, which pollute the environment. In order to use these substances for the benefit of production and minimize the burden on the environmental situation, a waste heat boiler was invented.
Description of the types of waste heat boilers
The operation of heat exchange units is based on the transfer of energy available in hot gas masses to a liquid heat carrier. A recovery boiler is usually not equipped with a burner, since its design does not imply heating and combustion of fuel resources. On the other hand, a glow plug and a block are built into it, which ensures the artificial movement of gas along the internal paths of the boiler unit. Devices differ in a number of characteristics: they are single- and double-circuit, with different dimensions of the heating tank.
Depending on the flue gas temperature, the units can be divided into low and high temperatures. Indicators up to 900 ° С fall into the first category, indicators exceeding 1000 ° С fall into the second category.
According to the principle of operation, waste heat boilers can be divided into two classes. Steam units are used to generate hot steam for heating or industrial use. Hot water devices receive gases that leave the installation and transfer their heat to the water. The latter can be used for heating or other purposes.
Steam devices and boilers designed for heating water can be equipped with a combustion chamber. Since the recycling of masses of gases that would otherwise enter the atmosphere generates a lot of energy, such boilers are sometimes used to generate electricity. There are models that are not equipped with a firebox. In such devices, gases act directly on a heat exchanger with liquid or steam.
All structural elements in which combustion processes take place are made of fire-resistant materials.
Equipment set
Reorientation of a manufacturing enterprise or its development of new areas of activity may require additional technical devices. It may include the following elements:
- protective devices: heat-resistant shielding, safety blocks, shut-off valves, suspension parts;
- pump equipment;
- devices that provide ventilation and injection of air masses.
Some multi-component systems also use fittings from the plumbing arsenal. They are needed for the design of various types of heat exchange devices.
In some situations, it is advisable to purchase an uninterruptible power supply. A number of models are designed for the connection of a burner.
Specifications
The use of waste gas in full allows boilers to have high efficiency rates. For devices operating on liquid or solid fuels, they are significantly smaller. However, if the heat exchange surfaces are heavily clogged, the efficiency of the unit will decrease.You can clean these parts of the structure by washing with water or blowing steam. Vibration cleaning technology is also practiced.
Different types of boilers are used in different industries at certain stages of the production cycle. They differ in the number of steam generating registers, power parameters, circulating circuits used, and demands on the quality of the coolant.
How efficiently the unit will work depends on the type of supply, the amount of gas masses and their temperature. The volumes of waste emitted by different types of industry differ. The largest amount is formed during oil refining and metallurgy. The charge gas is specific for the latter. The presence of metal scale is favorable for burning gas fuel.
Advantages and disadvantages
The considered devices differ from other types of boiler units by the absence of the need for additional fuel. The heat recovery unit operates only on gas waste. This allows the fuel to be used much more efficiently and also reduces the cost of cleaning up the exhaust. In addition, the use of such boilers at enterprises has a positive effect on the environment. Energy emissions are significantly reduced. By reducing the volume of fuel containing hydrocarbons burned, significantly less greenhouse gases are released into the atmosphere. An energy-efficient production cycle reduces costs for the company.
Cold parts of the unit corrode. The efficiency of utilizing the heat exchanger depends on the temperature to which the generated gases are heated.
Features of work
During the operation of the boiler, its heat exchanger is covered with substances contained in the flue gases. This does not in the best way affect the efficiency of the utilizer. To make the efficiency as high as possible, a VOC thermal oxidizer can be installed in front of it.
If the demand for the use of waste gas heat arises only from time to time, it is possible to regulate the flow of emissions to the boiler. For this, a special bypass is used - a block that redirects waste to the chimney. The bypass function can be controlled by a dry contact, open and locked, or by using an external analog signal. In the latter case, the process is tied to the regulation of the opening angle of the damper.
Application area
It is advisable to install utilizers if, as a result of a certain process, a lot of physical heat is released, which must be further used to reduce fuel costs. This includes quenching hot coke and running gas turbines. In the latter case, the boiler is used to generate steam, which is subsequently used to heat the enterprise or to solve technological problems.
There are also modifications of the convective type, sharpened for the task of cooling carbon gases. They are used for melting steel. The design features of these units provide a large number of artificial circulation cycles and two-stage evaporation. Some boilers burn carbon oxide. Cooling of converter waste reduces entrainment and air pollution.
In thermal power plants, improved versions of the utilizers are used. Deaeration devices of atmospheric pressure are used to prepare water feeding the heating and hot water supply systems. They are also involved in the preparation of a heat carrier for steam boilers. For vacuum deaeration, secondary gas masses released during the operation of the turbine are used. The result is steam, which is subsequently reused in the turbine plant. This saves fuel resources.The steam generated is often at a high pressure.
The use of recyclers in the production cycle brings a number of useful effects: fuel is consumed more efficiently, the supply of heat energy and harmful compounds to the external environment is significantly reduced. When working with gases of sufficient temperature, the units have a very high efficiency.
