Whereas WHG is a kind of system using waste heat from the plants of cement, glass, iron and steel, metallurgy, ore heating furnace and carbon furnace. According to the characteristics of the heat resource and process requirements, We design an suite of optimized waste heat generation system and develop the key equipments such as the waste heat boiler and so on.
According to the characteristics of the waste heat resources of from the cement industry plant, we developed a new low temperature waste heat power generation technology and process on the basis of the step utility of waste heat resources and the principle of smallest available enthalpy loss. The technology has been used in a lot of 2500 -5000t/d new dry-process cement production lines. For further utility of the low temperature waste heat, we adopted dual pressure or flash system, and gained a good uprating in power output.
General WHG Process Flow Chart Revised-I
WHG Technology and Process
The ore sintering process is the major energy-consuming process in the iron and steel, and metallurgy industry, and almost accounts for 10% of the whole energy consumption. In a normal sintering plant, the waste heat from the cooler (ring cooler and straight cooler) accounts for 19%-35%, the potential use of the waste heat from the cooler is huge. Proved by theory and engineering practice, the step utility of the waste heat for power generation from the cooler is workable and economic with ensuring the sintering system working normally.
Cooperating with some companies from the iron and steel industry, we developed the Dual-Pressure WHG process and technology and the Dual-Pressure WHG process and technology with make-up Combustion in ore sintering process. These two WHG process adopt the exhaust flow gas recycling. In order to full use of the waste heat resources, the exhaust flow gas from the boiler with the temperature of 150-200℃ is recirculated to the wind pool to improve the outlet flow gas temp.of the cooler.
WHG Process Flow Chart 1 of Ore Sintering Process
WHG Process Flow Chart 2 of Ore Sintering Process
At the most condition of the operating WHG power plants in cement plants, the waste air temperature from the middle opening of the cooler is within the scope of 380-400℃, or even higher. When the flue gas temp. from C1 preheater is lower than 330℃, The superheated steam from PH boiler(general the steam temp. is lower than 300℃) will be sent to a high temperature general superheater(GSH)in the AQC boiler. Then the steam from PH boiler, together with that of AQC boiler, is heated to higher temperature. Usually this mixed steam is heated to 360-380℃, which is 50-60℃ higher than that in the general process. Usually, the electricity output efficiency of the Modified I process is 5-80% higher than that of the original process.
Revised -II WHG Technology and Process
Step utilization is considered for the waste heat from the grate cooler. There are two suction openings in the middle of cooler. The high temperature flow gas from one opening is about 480-500℃, and the other is about 300-380℃. The mixed low temperature superheated steam from AQC and PH boiler will be heated to approximately 430℃ by the high temperature flow gas. The WHG power output of this process is approximately 8-15% higher than that of general process.
The general technology and process is widely used in waste heat generation of cement plant. In the Revised-I and Revised-II technology and process, we gives attention not only to maximize the superheated steam production, but alsoto increase the steam temperature. The step utilization of waste heat flow gas is adopted, and the power output of the superheated steam is increased, the two kinds of revised technology and process are our patents .
The three kinds of technology and process as mentioned above can adopt single pressure, dual pressure or flash system to fully utilize waste heat resource, and the outlet waste gas temperature from AQC boiler will be reduced to 80-100℃. the outlet waste gas temperature from Ph boiler will be reduced to the need temperature of cement product process.
Revised-II WHG Process Flow Chart
Dual pressure system is a dual pressure waste heat boiler and steam up condensing steam turbine to fill low-pressure superheated steam to steam turbine, raising the utili-zation rate of waste heat and improve power generation efficiency.
If there is surplus gas in pipeline network, a single or dual pressure system with make-up combustion can be adopped in Figure 3 and 4. A make-up combustion power generation process is adopted with making use of surplus gas, a single/dual pressure boiler with high temperature superheater is equipped, and the steam consumption of turbine can be reduced, this process can increase the power generation, and reduce the system fluctuation.
WHG Process Flow Chart 3 of Ore Sintering Process
WHG Process Flow Chart 4 of Ore Sintering Process
WHG system with make-up combustion system and dual pressure boiler will further improve the waste heat utility efficiency.