A Technical paper on
“Co-generation”,
“Combined Heat and Power (CHP)”
Suresh Kolamala
Energy management Cell
R I L, A TATA Entriprize
Abstract
The main objective of this technical paper on co-generation, combined
heat and power brings about the need of the co-generation to meet the
present demand of electricity. It also bridges the gap between supply and
ever increasing demand of electrical energy and becoming self reliant in
terms of captive electrical power rather depends on the state grids. It also
talks about the co-generation technology, benefits, applications and
potential beneficiaries for the amateurs who are keen to implement this
technology to meet their needs and serves nation as a whole by reducing the
load on grids and reduction of CO2 emissions to protect the environment.
It is followed by case study of 1 MW tri-generation reciprocating
natural gas based engine, which includes scenario and costs before and
after installation. Our experience and benefits from this co-generation
system is also included along with our comments/suggestions to potential
aspirers.
Contents
1. Introduction
o Definition
o Need of co-generation
o Benefits of co-generation
o Applying co-generation
o Potential users of co-generation
o Technical options of co-generation
2. Case study – 1 MW Captive power plant (GE Jenbacher) at our
location
3. Conclusion
4. References
1. INTRODUCTION
1.1 Definition
Co-generation is defined as the sequential generation of two forms of
useful energy from a single primary energy source, typical two forms of
energies are mechanical energy and thermal energy. Mechanical energy may
be used may be used to either to drive an alternator to produce electricity or
rotate an equipments like motor, compressor, pump or fans etc., for
delivering different services. Thermal energy may be used directly for the
process for heating purpose or indirectly to produce the steam generation,
hot water or hot air for dryer and chilled water generation for process
cooling.
Generation of three different forms of energy from the single primary
energy source is called as Tri-generation, i.e., generation of Electricity,
Steam or Hot water and Chilled water from single source of primary fuel.
Above both systems is also called as “Total Energy System”
1.2 Need of co-generation
Thermal power plants are major sources of electricity supply in India.
The conventional method of power generation and supply to the customer is
wasteful in the sense that only about a third of the primary energy fed into
the power plant is actually made to available to the user in the form of
electricity (Figure 1). In conventional power plant, efficiency is only 33% and
remaining 65% of energy is lost. The major loss in the conversion process is
the heat rejected to surrounding water or air due to the inherent constraints
of the different thermodynamic cycles employed in power generation. Also of
further losses of around 10-15% are associated with the transmission and
distribution of electricity in the electrical grid.
Through the utilization of the heat, the efficiency of the co-generation
plant can reach 90% or more. In addition, the electricity generated by the
co-generation plant is normally used locally, and then transmission and
distribution losses will be negligible. Co-generation therefore offers energy
savings ranging between 15-40% when compared against the supply of
electricity and heat from the power stations and boilers.
Figure 1: Balance in a typical coal fired power station
(For an input energy of 100 Giga joules (GJ))
1.3 Benefits of co-generation
Provided the co-generation is optimized in the way described above,
the following benefits arise as co-generation is a well proven technology,
recognized world over as a cleaner alternative to traditional centralized
generation. Its long term future in the global energy markets is secured by
its ability to provide operational, financial and environmental benefits from t
a single unit of a fuel.
Operational advantages:
Base load electrical supply
Security of supply
Increased diversity on heating and hot water
Steam raising capabilities
Tri-generation, using absorption/mechanical chillers for cooling
Financial advantages:
Reduced primary energy cost
Stabilized electricity cost over a fixed period
Flexible procurement solutions
Reduced investment in surrounding plants eg. Boilers
Environmental advantages:
Improved fuel efficiency
Reduced CO2 emissions
No transmission losses
Lower SOX emissions with the use of Natural gas as a fuel
1.4 Applying co-generation
Consistent demands for the thermal energy, and considerable
electrical base loads are most appropriate for co-generation. One can
consider the co-generation in the following cases of situation.
Designing a new building
Installation of new boiler plant
Existing site re-development
Continuity of power supply
Increasing energy efficiency
Improving financial performance
Positive environmental effect
Supporting the company’s green image
1.5 Potential users of co-generation
Co-generation has a long history of use in many types of industry,
particularly in the pulp & paper and bulk chemicals industries, which have
large concurrent heat and power demands. In recent years the greater
availability and wider choice of suitable technology has meant cogeneration
has become an attractive and practical proposition for a wide range of
applications. These include the process industries, commercial and public
sector buildings and district heating schemes, all of which have
considerable heat demand. These applications are summarized in the table
below. The table also list renewable fuels that can enhance the value of cogeneration,
although fossil fuels, particularly natural gas, more widely used.
Possible opportunities for application of co-generation:
Industrial
Pharmaceuticals and fine chemicals
Paper and board manufacture
Brewing, distilling and malting
Ceramics
Brick
Cement
Food processing
Textile processing
Mineral processing
Oil Refineries
Iron and Steel
Buildings
District heating
Hotels
Hospitals
College campuses and schools
Airports
Supermarkets and large stores
Office buildings
1.6 Technical options for co-generation
Co-generation technologies that have been widely commercialized
include extraction/back pressure steam turbine, gas turbine with heat
recovery boiler and reciprocating engines with heat recovery boiler.
1.4.1 Steam turbine co-generation systems
Two types of steam turbine most widely used are the back pressure
and extraction-condensing types (Figure 2). The choice between back
pressure turbine and extraction-condensing turbine depends mainly on the
quantities on the quantities of power and heat, quality of heat and economic
factors. The extraction points of steam from the turbine could be more than
one, depending on the temperature levels of heat required by the processes.
Figure 2: Schematic diagrams of steam turbine co-generation systems
The specific advantage of using steam turbines in comparison with the other
prime movers is option for using a wide variety of conventional fuels as well
as alternative fuels such as natural gas, fuel oil and biomass.
1.4.2 Gas turbine co-generation systems
Gas turbine co-generation system can produce all or part of the
energy requirement of the site, and the energy released at high temperature
in the exhaust stack can be recovered for various heating and cooling
applications (Figure 3). Though natural gas is most commonly used, other
fuels such as light fuel oil or diesel can also be employed. The typical range
of gas turbines varies from a fraction of a MW to 100 MW.
Figure 3: Schematic diagrams of gas turbine co-generation systems
1.4.3 Reciprocating engine co-generation systems
It is also known as internal combustion engines, these co-generation
systems have high power generation efficiencies in comparison with other
prime movers. There are two sources of heat recovery: 1) From exhaust
gases at high temperature and 2) From engine jacket cooling water system
at low temperature (Figure 4). As heat recovery can be quite efficient for
smaller systems, these systems are more popular with smaller energy
consuming facilities, particularly those having a greater need for electricity
than thermal energy and where the quality of heat required is not high.
Figure 4: Schematic diagrams of reciprocating engine co-generation systems
2. CASE STUDY
This case study pertains to a chemical industry engaged in
manufacture of agrochemicals and related intermediates and having
manufacturing locations all across India. The technical grade product
manufacturing activity of this organization involves various equipment /
machineries driven by electrical energy. One of such site located in Gujarat
is having an approximate maximum demand of electricity up to 1.35 MW,
Steam requirement up to 2.5 TPH and Chilled water @ 5 deg C up to 90 TR.
The high cost of power coupled with the cost for generation of steam
and chilled water of desired temperature was eating into the bottom line of
the products in the highly competitive market. A cost effect analysis pointed
to power cost as the main target to work upon. Captive generation of power
as a stand alone project either using conventional or new generation fuels
was calculated to be not that cost effective. Since the three resources
required by the unit had some common features that are interdependent,
the study turned to a system that can cater to all the three utilities in
totality.
After much exploration into various technologies available in the
market, the management decided to go for a captive power plant with trigeneration
to meet the above requirement so as to reduce the utility cost of
the products and thereby making the products price competitive in the
market.
Scenario before installation of co-generation plant:
The above requirement is fulfilled by state electricity, 3 Ton steam
boiler and Vapor compression refrigeration of reciprocating compressor of
CHW systems.
Cost to the company before installation for the above requirement as
follows,
Equipment
Fuel/Electricity
consumption
(per hour)
Unit
cost
(Rs)
Cost per
hour
(Rs)
Total cost per 8000
hrs of year
(Rs Lacs)
Grid power 1064 kWh 5.5 5852
Boiler 195 Nm3/h 9.7 1892
CHW system 95 kWh 5.5 523
DG Set* 60 lit/h 35 2100
744
Notes:
1. Contract demand of grid power 1700 KVA
2. Maximum demand of plant 1350 KVA
3. CD charges per month 2.1 Lacs
4. Cost of unit power(kWh) (Average) 5.5 Rs
5. Total power bill per 8000 hrs 593 Lacs
6. * Exclusively for one critical reactor for 12 hrs running per day per
batch as grid power is not reliable and is not desired by the reaction.
Selection criteria for choosing the reciprocating machine:
An aspect – impact analysis was carried out in the course of selection of
the right type of technology that would be most appropriate for the unit
keeping in mind the modes of benefits specifically required in contributing
to savings. The following aspects were considered and vetted during
selection of engine by an expert team of 4 members.
1. The said team identified and visited those locations where captive
power plants have been already installed and had detailed discussions
with the users and their experiences were captured for evaluation and
as a learning process.
2. Team also learned about the 2-3 failures of other type of machines in
and around the location and recorded about that type engine (the
name of the engine is not mentioned in the light of code of conduct)
3. Coincidently one of our senior managers had some hands on
experience with this type of reciprocating engine.
4. It is the triple effect requirement of three utilities, namely Electricity,
Steam and Chilled water that prompted for selection of tri-generation
system. Had it not been so selection would have been for cogeneration
system
5. Since the company is a an enterprise of a big business group,
information from group companies could be gathered and taken into
consideration at the finalization stage of this project
6. A comparative study based on the techno-commercial aspects rated
reciprocating engine as the lowest cost and high returns system.
Scenario after installation of co-generation plant:
A reciprocating gas machine from GE Jenbacher installed with the
following parameters on June 2006.
1. Generation of electrical energy at full load – 1064 kWh
2. Generation of steam at full load – 1 TPH
3. Generation of CHW (Inlet -11 0C & Outlet – 6 0C ) – 92 TR
Reciprocating engine of GE Jenbacher is being operated with natural gas as
a primary fuel. The schematic diagram of tri-generation system is shown in
the figure 5.
Figure 5: Schematic diagrams of tri-generation of reciprocating engine cogeneration
systems
Equipment
Fuel/Electricity
consumption
(per hour)
Unit
cost
(Rs)
Cost per
hour
(Rs)
Total cost per 8000
hrs of year
(Rs Lacs)
Captive power 1064 kWh 3.3 3511
Grid power 285 kWh 5.5 1568
Boiler 125 Nm3/h 9.7 1213
CHW system** NIL - DG
Set*** NIL - -
503
Notes:
1. Contract demand of grid power 700 KVA
2. Maximum demand of plant 1350 KVA
3. CD Charges per month 0.62 Lacs
4. Cost of unit power(kWh) (Average) 5.5 Rs
5. Total power bill of grid electricity per 8000 hrs 126 Lacs
6. ** VCR system of compressor is stopped completely
7. *** As co-generation power is reliable, load of critical reactor
connected to co-generation plant.
Net savings per year, Rs Lacs **** 259
Cost of captive power plant , Rs Lacs 350
Simple payback period, Months 16
Month and year of commissioning of system June'2006
Actual accrued savings till Feb'2007,Rs Lacs # 138
Important notes:
1. **** Net savings are calculated by assuming 8000 hrs of operation per
year.
Net savings = Cost difference between grid and captive electricity
+
Reduction in contract demand charges
+
Elimination of compressor in VCR of CHW generation
+
Elimination of costly HSD fuel through stopping of DG set
2. # Due to delayed commissioning of VAM system, surrendering of grid
power, stopping of DG set and part loading of three generations
(Electricity, steam and Chilled water) savings are minimized.
Efficiency of generation of three utilities:
Form of energy
Efficiency on
Fuel
Electrical power 42%
Steam generation from exhaust gases 26%
CHW generation from jacket hot water 13%
Total efficiency on fuel input 81%
Advantages with GE Jenbacher Reciprocating engine:
High power efficiency achievable over a wide range
Relatively low cost per kWh electrical power output
Wide range of unit sizes from 3 kWh and upward
Part load operations from 30% to 100% with high efficiency
Fast start-up time of 15 second to full load (gas turbine needs 0.5 – 2
hrs)
Real multi fuel capability, it can also use FO as fuel
Can overhaul in site with normal operators
Can be operated remotely
Problems (with recommendations) faced during initial stage of
commissioning:
Some unforeseen problems and delays occurred during executing of captive
power plant
During installation of power plant and WHR unit:
Delay by 15 days has occurred in civil construction works due to
water fountain during excavation and non availability of required
manpower due to festivals, etc.,
This can be avoided by better project management schedules
after taking into the considerations festivals and etc which can be
avoided during project period.
Modifications based on the boiler inspector suggestions after
installation of WHRU
This delay can be avoided by approaching boiler inspector
prior to the installation of WHRU
Completion of all statutory requirements
This delay can be minimized by proper planning and followup
with concerned departments and officers
During installation of VAM system:
VAM system could not be commissioned along with power generation and
steam generation unit due to following reasons,
Miscommunication between engine makers and VAM makers.
VAM makers recommended certain changes in High Temperature hot
water from engine jacket, and it has been done later on tool ample
amount of time as we were to import the particular thermal element.
The above mentioned delays can be minimized well with the
proper planning and felicitation of discussions between
suppliers of other accessories with engine suppliers.
Benefits achieved since inception of project:
Monetary: Rs 138 Lacs has been saved and it has helped to improve
the bottom line of the company.
Self reliance: Self reliance in terms of captive electric power achieved
and it has helped to improve the productivity as there is no break
down of the plant due to power outages.
Reduction of CO2 emissions: Total quantity of 1326 Tons of CO2
emissions reduced as on end of Feb’2007 Vs potential of 7992 Tons
per year at 100% load.
CDM Benefits: Reduction of CO2 emission could be traded with World
Bank as per Kyoto protocol. These benefits will be exploited soon by
submitting a detailed project for our all initiatives in this regard.
SH&E policy: Helped to stick and work towards our SH&E policy for
greener environment.
Serving nation: By reduction of 1 MW load on the state grid, helped
nation to bridge the gap between supply and demand
3. CONCLUSION
Co-generation is well proven technology, recognized world wide as a
cleaner alternative to traditional centralized power centralization and it is
highly energy efficient whereas tri-generation applied in our case is
upcoming technology having higher efficiency than typical cogeneration
system delivering a number of positive financial and environmental benefits.
This will help to any organization individually and nation as a whole.
From the case study we have seen, it was evident that the cogeneration
and tri-generation system would substantially reduce the
operating cost of industries. The rate of return for this tri-generation project
is very attractive and payback period would fall in between 1 to 2 years.
Further in today’s the growing concern towards global warming and
cleaner development mechanisms, most of the CO2 emissions stem from the
burning of fossil fuels for the purpose of electricity generation. Coal
accounts for 93 percent of the emissions from the electric utility industry.
Going for Co-generation and tri-generation will substantially reduce CO2
emissions when compared with traditional heat and power generating
stations.
Thus, apart from monetary savings, Co-generation is a cost effective
way to conserve depleting fossil fuels and contributing to sustainable
development. Climate change and carbon emission reduction is an
increasingly dominant factor in co-generation’s future.
By seeing the above mentioned success and advantages with trigeneration
plant, it is strongly recommended the aspirers to go for the
implementation of this system and get benefited in terms of monetary and
environmentally.
4. REFERENCES
1. Energy efficiency in Thermal utilities – BEE
2. A Guide to co-generation – EDUCOGEN
3. GE Jenbacher manual