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Why CCHP system is energy-saving and economical?

1、The Generation and Development of Gas Combined Cooling Heating and Power Technology

With the increasing development of the world economy, energy shortages and environmental issues are becoming increasingly prominent. It has become a consensus among governments of various countries to vigorously develop and expand various types of energy, adjust the energy supply structure, and meet the energy needs of human production and life.

With the great expansion of human activities in depth and breadth, various issues related to the treatment of combustible gases have also attracted people’s attention, such as natural gas, shale gas, biogas, petroleum-associated gas, coalbed methane, biomass gas, and other combustible gases, which are also high-quality high calorific value gases. Combustion and utilization can meet the urgent energy needs of humans and reduce air pollution.

The Combined Cooling Heating and Power (CCHP) technology is based on energy cascading utilization and is a comprehensive energy supply system that systematizes the heating (heating and hot water supply), refrigeration, and power generation processes. The system fuel is combustible gas with a certain calorific value, and the comprehensive energy utilization efficiency is over 70%. It is known as the “second generation energy system” and has received attention from many developed countries and regions such as the United States and Europe, it has been extensively developed and utilized.

2、What are the characteristics of CCHP technology

Gas internal combustion generator sets generate high-temperature and high-pressure gas through the combustion of combustible gas by the engine. This gas drives the piston to move, drives the crankshaft to rotate, and achieves energy conversion and mechanical power output. The engine drives the alternator to rotate through a coupling, achieving power generation. Along with the power generation, there is a large amount of high-value available waste heat. Through the waste heat conversion device, the combined supply of cold, heat, and power can be achieved.

2.1Improve overall energy utilization efficiency

By applying the principle of energy cascade utilization, waste heat is utilized while generating electricity, achieving a cascade utilization of energy from high-grade to low-grade, greatly improving the comprehensive utilization efficiency of primary energy and significantly increasing benefits. The power generation efficiency of large power plants is usually 30% to 40%, and long-distance transmission incurs power consumption; The comprehensive energy efficiency of using a combined cooling, heating, and power system can reach 80% to 90%.

PowerLink’s 2000kW biogas cogeneration project in China uses four CG500C-BG biogas cogeneration units, which can output 2000kWe of electricity per hour and are accompanied by recyclable heat output. The overall system efficiency is as high as 86.5%.

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Figure 1 PowerLink China 2000kWe biogas cogeneration project

2.2 Located nearby and self-use spontaneously

The CCHP system is generally arranged inside buildings, close to end users, and the generated cold, heat, and power energy is directly supplied to users. It can operate at any time and can be adjusted flexibly and conveniently, effectively avoiding energy losses caused by water conservancy imbalance and uneven cooling and heating in large-scale thermal and power projects.

2.3 Reduce air pollution and protect the environment

The important auxiliary equipment for the configuration of the combined cooling, heating, and power system is the lithium bromide absorption refrigeration unit. The lithium bromide refrigeration unit replaces the compression refrigeration unit, which can avoid the use of Freon refrigerant, reduce the use and discharge of a large amount of Freon, and is conducive to environmental protection.

3、Environmental protection, energy conservation, and economic efficiency of the CCHP system

The large amount of combustibles produced in human production and life are mainly composed of methane and carbon dioxide. According to a report from the Ritchie National Laboratory in the United States in 1997, the concentration of carbon dioxide in the atmosphere has increased by 30% since the Industrial Revolution, methane has doubled, and nitrogen oxides have increased by 15%. Carbon dioxide, methane, and nitrogen oxides are all gases that can generate the greenhouse effect. The increase in their concentration leads to global temperature rise, glacier melting, and a deteriorating atmospheric environment.

3.1Environmental Protection and Energy Conservation of CCHP System

The combined cooling, heating, and power technology reduces methane emissions by burning methane in combustibles, which is beneficial for improving air quality. The electricity and cold/hot energy converted from combustion can also provide some energy to meet people’s production and living needs, thereby reducing the consumption demand for coal, saving energy, and playing a role in carbon reduction, environmental protection, and energy conservation.

According to Chinese experts, based on the current number of buildings in China, if the proportion of CCHP is increased from 4% to 8%, CO2 emissions will be reduced by 30% by 2020, which is of significant significance for reducing global greenhouse gas emissions

3.2Excellent economic performance of the CCHP system

The cogeneration system of cold, heat, and power is usually located near the end users, and the transportation energy consumption is close to zero. However, traditional large-scale coal-fired thermal power plants consume a lot of resources, and long-distance transmission of electricity and heat (cold). They also require a large transmission and distribution system, which has high economic costs and poor economic efficiency.

Taking the PowerLink ACG20S unit as an example, we can compare the economic differences between traditional energy supply and distributed cogeneration methods.

Traditional power and heat supply
Energy mode Grid+

Electric water heater

Grid

+Natural gas boiler

Grid

+Air source heat pump

Power supply mode Grid Grid Grid
Heat supply mode Electric water heater NG water heater Air source heat pump
Hot water (1.0t@∆t=20℃)  25kWhe 2.6 m3  NG 6kWhe
Heat cost (1.0t@∆t=20℃) 3.7 $ 1.15 $ 0.88 $
Power cost (20kWe) 2.9 $ 2.9 $ 2.9 $
Total cost 6.6 $ 4.05 $ 8.9 $

 Distributed energy supply  (one ACG20S natural gas unit for power supply and heating):

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Note: The above numerical calculations are based on the current average energy price in Shanghai: 1.0 yuan/kWe for electricity and 3.0 yuan/m³for natural gas.

Through comparison, it can be found that the total cost of the distributed cogeneration energy supply for gas internal combustion generator sets is only 2.6$, which is more cost-effective compared to the three traditional energy supply modes.

4、Common configuration methods and applications of combined cooling, heating, and power systems

4.1What are the common configuration methods for CCHP systems

There are two common configuration methods for cogeneration systems:

One is a gas generation unit +waste heat boiler+ lithium bromide refrigeration unit, which usually supplies energy such as electricity, steam, and cooling to end users. Steam is generated by the waste heat boiler through the recovery of high-temperature flue gas heat generated by the gas unit.

Another type is a gas internal combustion generator set + waste heat recovery device+ lithium bromide refrigeration unit. The waste heat recovery device in the system can usually be selected as a waste heat boiler or heat exchanger. If steam is needed, a waste heat boiler can be configured for heating. If hot water is needed, it can be exchanged and recovered through a heat exchanger. The lithium bromide refrigeration unit can convert heat for cooling to users.

Figure 2 shows the natural gas CCHP system diagram produced by PowerLink company. Through the combustion of natural gas in a natural gas internal combustion generator set and energy conversion, it can provide end users with energy such as electricity, cold air, and heat.

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Figure 2 Natural Gas CCHP System Diagram

Compared with the gas turbine unit, the internal combustion engine unit has a higher power generation efficiency, resulting in a higher proportion of electricity output in the internal combustion engine combined cooling, heating, and power system. The cold to electricity ratio is usually 1.0-1.5. In terms of price, the internal combustion engine unit has a more cost-effective advantage. Therefore, the gas internal combustion combined cooling, heating, and power system is widely adopted.

 

4.2Application site of CCHP system

The CCHP system requires less land and is usually flexibly located on the user side. It can mainly be used in commercial, industrial production, urban buildings, hotels, airports, hospitals, schools, residential communities, bathing centers, entertainment clubs and other places.

5、Conclusion

The gas CCHP system can be distributed on the user side and can flexibly provide energy such as cold, heat, and electricity to end users. It has the characteristics of high comprehensive efficiency, flexible configuration, energy conservation, environmental protection, and good economy. It is a mature and reliable high-quality energy cogeneration system.

 

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