WHR

Our world has been rapidly developing and industrializing. In many industrial plants, waste heat is developed due to the internal processes. The flue gases emitted from the stack to the atmosphere lead global warming and air pollution; and consequently pollution of underground water and destruction of natural flora. Today, it is possible to collect these gases and to produce electricity from them in an efficient way. SC Industry Inc. bring so called Waste Heat Recovery systems (WHR) in our country depending on the appropriate conditions and depreciation circumstances.

“Waste Heat Recovery is a method which is used for generating electricity from the useless heat formed in the high temperature processes in various industries such as cement, iron-steel and glass. These systems became very popular in Japan in 70s  and in China as well thanks to the governmental incentives and enforcements in the late of 90s and have been commonly used in world wide today. The energy which is generated by using WHR systems is economic and environment friendly. The utilization of WHR systems in the industry has been gradually increased in parallel with the increase of the energy prices and awareness for energy efficiency.

WHR systems have direct and indirect benefits:

    It enhances the energy efficiency of the process.

    Due to the decrease in the temperature of the flue gas, loads and dimensions of the equipment, e.g. stack, fans, can be lowered.

    Energy is saved and thereby the product cost.

    Use of an environmental friendly system will change the image of the factory.

Single stage, double stage or strobes boilers are used in WHR systems with traditional steam technology. WHR system consists of a boiler(s), turbine, generator, dedusting chamber, cooling tower and chemical treatment unit.

(Picture- WHR system with strobe boiler)
 

Steam is generated in the boiler by utilizing the thermal power of the flue gas having a high heating value. Afterwards this steam is directed to the turbine and electric power is generated by means of the generator. The water coming from the turbine outlet is cooled down and sent to the chemical treatment unit for re-use.

The flue gas in cement plants is obtained from two different locations: firstly, from the midpoint of cooling unit at the outlet of rotating furnace and secondly, from the pre-heater. The gas coming from the cooling unit is passed through a high efficiency dedusting chamber prior to transferring to the boiler, so that the dust load is lowered

In WHR system design, several points should be considered: location of the plant, production capacity, waste heat parameters, water analysis, climatic conditions, geological conditions and particularly room dimensions required to install the system inside the plant. These factors have impacts on the selection of technology and equipment to be used.
 

SAMPLE STUDY

     A WHR system will be installed in an integrated cement plant with a capacity of 3000 tons/day. It has a 4-staged furnace equipped with pre-heater and pre-calcinator. The humidity of the raw material is less than 3%. The solution of the system was made with strobe boiler and the installed power was foreseen as 5MW. The thermal efficiency of this system will be 22%. The cost of  said investment is estimated as 10 million USD and it is expected to be completed within 18 months.

     If the annual operation time of the system is assumed as 7000 hours, then 35.000.000 kWh will be produced annually. The income for this amount of electricity will be 3.500.000 USD/year (operation and maintenance cost of the system is estimated as 20 USD / MWh).

     If a saving of 65 tons CO2e/MWh is considered, then 22.750 tons less CO2 is emitted to the environment per year. In case of the sale of the carbon credit after getting license for carbon trade, then it is possible to obtain further income of 400.500 USD.

     When the investment is analyzed financially, the EBITDA margin, IRR and net present value are calculated as 79,98%, 38,24 and 13.447.101 USD respectively.

     As the system is environmental friendly, long term credits are provided by the European Environment Funds and World Bank. Certain banks in Turkey may provide credits with 4-year grace period and LIBOR+2 interest rate up to 14 years. The investment is in this sense very charming.