At present, waste heat utilization is widely used in the brick industry, however, the waste heat utilization is low, the waste is more serious, according to the survey, the total waste heat resources account for about 17% of its total fuel consumption 67%, the waste heat resources that can be used are about 60% of the total waste heat resources, and the actual utilization is only 366% or so.
There are many ways to use waste heat. Generally speaking, the first is the comprehensive utilization of waste heat; followed by direct utilization; The third is indirect utilization (generating steam to generate electricity).
Composition of kiln waste heat
In the waste heat of the kiln, there is both high-temperature air and high-temperature flue gas. At the same time, there is also cold hot air. The first task of the high-temperature exhaust gas flowing into the pre-tropical heat from the firing zone is to heat the green body and increase the temperature of the green body. Secondly, it should also transfer heat to the kiln wall and the top of the kiln, so that the temperature of the wall and the top is higher than the temperature of the brick, so that the green body will not dissipate heat outward and reduce the temperature, and at the same time, it will also transfer heat to the kiln car, so that the temperature of the kiln car will rise, so that the temperature difference between the kiln pre-heat will not be too large. After all the above heat has been used, the heat in the flue gas has not been used up, and a considerable part of the heat can be used for other purposes. If the heat is taken out in the higher temperature section of the pre-tropical zone, it can be obtained by the high-temperature smoke heat, which is the extraction of the high-temperature smoke heat of the pre-tropical zone. If the required heat is taken out in the low temperature section of the pre-tropical zone, it can be obtained by low-temperature smoke, which often extracts the low-temperature flue gas in the kiln.
In the kiln firing zone, all the waste heat in the kiln is used through the internal flow. However, due to the high temperature of the firing zone, the external temperature of the kiln top is also very high, and the heat lost through the kiln top is a lot. Some kilns adopt the method of forced ventilation heat exchange at the top of the firing zone, so as to obtain the waste heat at the top of the firing zone, due to the use of forced heat exchange, although the heat exchange effect outside the kiln is very good, the heat in the kiln has also increased significantly through the heat transfer to the outside of the kiln roof, so that the temperature in the kiln also has the phenomenon of low temperature conversion. Obviously, this method of exchanging heat from the top of the kiln is not advisable. Another method is to exchange the waste heat outside the kiln through the method of non-forced heat exchange, without affecting the normal heat dissipation from the inside of the kiln to the outside of the kiln. Although the heat exchange of this method is smaller, it has no impact on the normal of the kiln, and it is a better method to use the waste heat of the firing zone.
The air brought into the kiln by cooling is heated by a high-temperature special unit and becomes high-temperature air with a high temperature, and the air contains a high amount of heat. Since the air volume entering the firing zone as combustion air is only a part of the air volume supplied to the cooling zone, the other part becomes waste heat that is not used in the kiln. The amount of preheating is related to the location and flow rate of the extraction of waste heat, and the amount of extracted waste heat should also be considered according to the actual needs of the kiln.
To sum up, the waste heat of the kiln mainly includes the low-temperature smoke heat of the pre-tropical zone. , high-temperature smoke heat, heat dissipation from the top of the firing zone to the outside world, heat exchange and heat exchange of the cooling belt, mainly the heat contained in the high-temperature air.
How to use the waste heat of the kiln
The use of waste heat in the kiln can be divided into two types: direct use and heat exchange use. When used directly, there are clean air use methods that directly use high-temperature air and have relatively high requirements for the cleanliness of hot air, and there are also direct use methods that require relatively low cleanliness of the gas used. The other is the direct use method that has lower requirements for the hot medium used and is not afraid of gas corrosion. Both of these methods of direct use of heat energy in the gas can be used to dry bricks in a drying chamber. The use method of heat exchange is used in the work where the cleanliness of the air is relatively high, or the gas is not corrosive and the gas cannot cause damage to the equipment or metal pipelines. For example, in the production of high-grade wall materials, if the kiln is used to pre-heat the high temperature smoke heat, and can not cause pollution to the drying process of the wet billet, then the heat exchange method should be used to exchange the heat in the high temperature smoke heat, use it to heat the clean air, and then use the high temperature clean air to dry the green body, which not only uses the high temperature smoke heat of the kiln, but also will not cause pollution to the product. Another method of heat exchange using kiln waste heat is heat exchange between gas and liquid, using high-temperature gas to heat the low-temperature liquid, and then fully use it according to the use of the liquid, which not only uses the waste heat in the kiln, but also enriches the use of waste heat.
For high internal combustion or super internal combustion bricks, the water in the heat exchanger can be heated with a water tube waste heat exchanger to bring the water temperature to a certain level, which can be used as a heating heat source for the factory floor.
Summarizing the above, it can be seen that the specific use of waste heat is:
In the drying process, which has low requirements for medium quality, the high-temperature air of the cooling belt and the high-temperature flue gas of the pre-tropical zone can be directly extracted, and the bricks can be sent to the drying room to dry through certain facilities.
In the drying process with high requirements for medium quality, high-temperature air and high-temperature flue gas cannot be directly extracted for green body drying, but the waste heat in the kiln should be exchanged through a heat exchanger (heat exchanger) and then used in a certain way.
For the use of waste heat on the kiln for heating and bathing, it is necessary to use a heat exchanger to replace the heat in the kiln, use the replaced heat to heat the water, and use this heat through hot water.
For enterprises that use high calorific value coal gangue for production, because the calorific value of coal gangue itself is more than double the heat required for firing, if all the remaining heat is extracted and used to build a thermal power station, its power generation can be used for part or all of the production of the factory, and it can also provide electricity for the factory's daily life.
In addition to supplying the company, the waste heat in the kiln can also provide hot gas and hot water to nearby related enterprises as a heat source for the company's use.
Waste heat technology and method
1. Separated heat pipe waste heat technology;
2. Integral heat pipe waste heat technology;
3. Waste heat mode: The different design and method of waste heat can bring completely different results, that is, the amount of waste heat or steam volume is completely different.
Process selection of kiln waste heat utilization.
In accordance with the principle of high efficiency, low consumption and maximum possible utilization, combined with the actual situation of the unit, we set up eight sets of waste heat extraction pipes in the cooling section of the kiln, and set up cold air outlets at the confluence of the pipelines to adjust the air temperature in the pipes. Eight groups of pipelines are respectively located on the corresponding parking spaces of the cooling section of the kiln, and manual rams are set at the bends of the pipelines to facilitate operation. After the waste heat extraction pipe is converging, the waste heat is sent to the drying kiln through the fan to dry the bricks. The drying kiln is equipped with three sets of top air supply pipes and eight sets of side air supply pipes. The working principle of the drying kiln is that the vortex system extracts the hot air in the lower temperature section of the roasting kiln by the hot air supply fan, and sends it into the drying kiln from the top and side of the drying kiln in the higher temperature section of the drying kiln, forming negative pressure at the top and periphery of the channel, and forming a circumferential rotating wind in the same section of the drying kiln; Four exhaust fans at the end of the drying kiln form the main airflow of longitudinal movement in the kiln, and the circumferential rotating wind is superimposed with the main airflow of longitudinal movement in the channel, so that the air in the channel advances in the form of spiral wind; In the longitudinal direction of the drying kiln, each parking space has a top air supply, which can form a spiral air in the whole kiln; The spiral air has both longitudinal gas flow and circumferential gas circulation, so that the air temperature and humidity in the drying kiln channel can be kept uniform.
A group of heat exchangers are set on both sides of the kiln at the beginning of the cooling section, and the heat exchanger adopts a high-efficiency, maintenance-free bellows heat exchanger for staff bathing and winter heating. The principle is that the waste heat is exchanged with the water from the bellows through the heat exchanger, and then directly heated or used to heat the bathhouse water through the heat exchange between water and water as needed.