Cement equipment upgrading to increase the use of industrial waste heat
Date：2019-08-27 17:50 Source：cementepcViews:
At present, high temperature waste heat utilization technology has become increasingly mature, but the utilization rate of low and medium temperature waste heat is still very low.The proportion of medium and low temperature waste heat in the total residual heat is about 40% ~ 50%. If this part of energy can be used, it will not only save a lot of resources for the society, but also reduce the emission of carbon dioxide and heat pollution, promoting the improvement of ecological environment.
1. Introduction of waste heat utilization
Waste heat is secondary energy, is the fuel and primary energy conversion process after the product, is the working medium combustion process left unused heat.Waste heat not only depends on the quality of energy itself, but also depends on the development of production technology and scientific level.Hot water method, preheating air, waste heat boiler, flue gas - fluid heat exchanger and processing materials are all common waste heat utilization methods.
Due to different production methods, equipment, raw material and fuel conditions, and various technological changes, the waste heat utilization has caused a lot of inconvenience.The characteristics of waste heat sources can be roughly divided into the following categories:
(1) unstable thermal load.
It depends on the process.
(2) corrosion of heat source.
Most of the waste heat flue gas is made up of corrosive gases such as sulfur dioxide. In addition, all kinds of substances containing metallic elements and non-metallic elements in soot or slag may cause low temperature or high temperature corrosion on the heating surface of waste heat recovery equipment.
(3) subject to the conditions of the installation site.
For example, the requirements for equipment connection, smoke exhaust temperature within a certain range, and so on.These requirements are likely to limit the use of waste heat recovery equipment, need comprehensive research and consideration.
(4) waste heat flue gas has large dust content.
At the same time, the chemical and physical properties of soot are also very bad. When the furnace smoke temperature is high and the dust content is large, it is more likely to accumulate ash and bond, thus causing wear and even blockage of waste heat recovery equipment.
The waste heat utilization potential of industrial production process is great, but it is not a one-time thing, and it should meet the requirements of technological needs, economic rationality, technological feasibility and ecological civilization at the same time.The most fundamental problem is not waste heat recovery, but to reduce waste heat emissions as much as possible, such as reducing smoke exhaust temperature, reducing heat loss, thermal cascade utilization, reducing heat taken by cooling medium and improving thermal efficiency of thermal equipment.
Therefore, before formulating the waste heat recovery plan, the following points are required:
(1) check whether the thermal efficiency of the device can be improved.Improving the thermal efficiency of the plant can not only reduce the amount of waste heat and reduce energy consumption, but also be more effective and economical than adopting recycling device.
(2) consider whether waste heat can be returned to the device itself for preheating fuel or combustion air, etc.This saves high-quality energy, directly reduces energy consumption in the plant, and is more energy efficient than recycling waste heat for other USES, such as generating steam.
(3) formulate recycling plan.First of all, it is necessary to understand the quality and quantity of waste heat as well as user requirements, and try to match energy levels. Within the permitted scope of economic and technical principles, it is necessary to select appropriate systems and equipment, so as to make the best use of surplus and exert the best effect as far as possible.
2. Classification of waste heat resources
As one of the hot spots of energy conservation, waste heat utilization is widely distributed in various heavy industry enterprises and light industry enterprises.The storage of waste heat is very abundant. Due to technical or technological limitations, most enterprises fail to make effective use of this part of heat and discharge a large amount of heat into the atmosphere, which not only causes a waste of energy, but also may cause pollution to the ecological environment.
Waste heat resources can be classified into solid waste heat resources, liquid waste heat resources and gas waste heat resources according to different waste heat carriers.According to the different temperature of waste heat carrier, it can be divided into high temperature waste heat (above 500℃), medium temperature waste heat (200℃-500℃) and low temperature waste heat (below 200℃).According to the different sources of waste heat resources, it can be divided into high temperature flue gas waste heat, high temperature steam waste heat, high temperature product waste heat, high temperature slag waste heat, cooling medium waste heat, condensed water waste heat, combustible waste gas waste heat, chemical reaction waste heat and so on.
These waste heat energy can be further converted into other mechanical energy, electrical energy, thermal energy or cold energy by using certain technical means.
3. Recovery of waste heat resources
There are many ways of waste heat recovery, including power recovery and heat recovery.Power recovery is the use of waste heat energy to produce electrical energy or mechanical energy, so that low-quality thermal energy into high-quality electrical energy or mechanical energy.In most cases, it is used to produce electricity, a high-quality energy source with high applicability and easy transmission.Cement plant in China has a very mature low temperature waste heat power generation technology, namely the pure cement kiln low temperature waste heat power generation technology, the power station on the production line of heat boiler, the two general Settings respectively referred to as the kiln head and preheater waste heat boiler, waste heat boiler preheater in cement production process of using the kiln head and discharged or clinker out of a large amount of heat is introduced into waste heat boiler, through the heat recovery steam rose, then push the turbine power generator.This method can kill two birds with one stone by reducing the energy consumption of factories and reducing the pollution of the ecological environment.Heat recovery is the direct use of waste heat, using the process of recycling water waste heat in the factory with the help of heat pump technology to solve the building heating.This kind of recycling method that USES waste heat resources to directly produce heat energy or provide cold energy for use is called heat recycling.
4. Suggestions on waste heat recovery
(1) to develop the waste heat treatment technology, such as the new dry process cement kiln waste heat power generation technology without afterburning boiler, hot water power generation technology, waste heat power generation technology, float glass line converter waste heat power generation technology, etc., these techniques in the iron and steel, petroleum chemical industry, building materials, cement, nonferrous metals, sugar, and other fields have a wide range of applications.As long as the heat reaches a certain amount, it can be recovered by low-temperature power generation technology.
(2) strengthen research on the utilization technology of waste heat at medium and low temperature, and promote the development and application of waste heat utilization technology.We will encourage more energy-intensive enterprises to adopt energy-saving technologies, better understand them, and form a new clean development mechanism.
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