Part 2 CCT Overview
Co-production Systems

7A1. Co-generation Systems
Technology overview

1. Definition of co-generation
A co-generation system is a system using a common energy
source to produce both electricity and thermal energy for otheruses, resulting in increased fuel efficiency.
2. Co-generation systems
Co-generation systems are roughly divided into two types. One is

The former generally uses liquid or gas fuel and is often small-a type that powers a diesel engine, gas engine, gas turbine, orscale for hotels, supermarkets, and hospitals.

other motor to generate power while recovering the waste heat

As for the latter, every type of fuel, including coal, is used as fuelfrom the motor as hot water or steam through a thermal

for boilers and many are found as relatively large-scale industrial-exchange at a boiler. The other type involves generating power by

use thermal power plants. Systems are further grouped into ones

rotating a steam turbine with steam produced by boilers andthat mainly supply electricity (condensing turbines) versus thoseremoving steam of a desired pressure as process steam.

that mainly provide steam (back-pressure turbines).

Electricity

Jacket cooling water

Hot water

Diesel orgas engine

Waste heatrecovery boiler

Heating
Hot water supply

Cooling water
heat exchanger
Steam

Generator

Electricity

Process steam

StackFig. 1 Overview of a typical diesel/gas co-generation system

3. Efficiency
In general, the power generation efficiency of a coal thermal

wholesales/supplies electricity as an independent power

power generation plant producing only electricity is around 40%.

producer (IPP). Electricity generated from the No. 1 unit, which

On the other hand, the overall thermal efficiency of abegan operating in April 2002, and the No. 2 unit, which begancogeneration system, which combines power generation

operating in April 2004, are all being delivered to The Kansai

efficiency and heat recovery efficiency, depends upon whether its

Electric Power, Inc.

main purpose is to supply electricity or to supply heat. Co-(2) Regional supply of heatgeneration systems that primarily supply heat can reach

A portion of the steam from the Kobe plant to be used for power

efficiency levels as high as 80%.

generation is extracted in order to supply up to a maximum of 40(1) Co-generation at a large-capacity coal thermal power plant

tons/hr to four nearby sake-breweries. This amount, accounting

Kobe Steel’s Shinko Kobe Power Station, a 1,400MW (700MW x

for approximately 2% of the steam generated in the boilers,2

indicates that the share of heat supplied is small. Previously, eachgenerators),large-scalecoal

thermalpower

plant,

107

Clean Coal Technologies in Japanbrewery had produced its own steam. Now, however, the power
plant’s secondary steam is extracted at the steam header anddirectly supplied to the breweries. By using steam extracted
from the power plant, regional energy conservation efforts arerealized.
(3) Heat supply conditions
Steam extracted from the turbine of the power plant contains
trace amounts of a rust inhibitor called hydrazine and, therefore,cannot be directly supplied to breweries since the steam used in
the breweries comes into direct contact with rice. Secondary
steam, produced indirectly using a steam generator powered byturbine extraction steam (primary steam), is therefore supplied
to breweries. An overview of Kobe Steel’s Shinko Kobe Power
Station is shown in Photo 1.

Photo 1 View of Kobe Steel’s Shinko Kobe Power Station

No. 1 power plant
Steam
Boiler

TurbineGenerator

Extracted
steam
Feed water

Cooling water(Sea water)

Primary steam
Breweries

BackupNo. 2 power plant

Secondary steam

Sawanotsuru
Fukumusume

Steamgenerator

Hakutsuru
Industrial
water

Drain cooler
Industrial
water tank

Gekkeikan

Water supply processing

Fig. 2 Process flow of heat supply facility

References

1) Shibamoto et al., Featured Thermal Power Plant Thermal Efficiency Improvement, Article 3 Thermal Efficiency Management Trend;
Thermal Control for a Power Generation System, pp. 1242-1246, Vol. 54, No. 565, Thermal/Nuclear Power Generation, Oct. 2003.
2) The Thermal and Nuclear Power Engineering Society: Introductory Course IV. Industrial-Use Thermal Power Facilities, Etc., pp. 15391546 Vol. 54, No. 567, Thermal/Nuclear Power Generation, Dec. 2003.
3) Kida et al., Outline of Power Generation Facilities at Kobe Steel’s Shinko Kobe Power Station, pp. 2-7, Vol. 53, No. 2, Kobe SteelTechnical Report, Sept. 2003.
4) Miyabe et al., Kobe Steel’s Shinko Kobe Power Station Surplus Steam-Based Heat Supply Facility, pp. 14-18, Vol. 53, No. 2, KobeSteel Technical Report, Sept. 2003.

108