Combined Heat and Power Concept. Dr. Oscar L. Jimenez Energy Project Manager. GEPROP.

Combined Heat and Power Concept.

Dr. Oscar L. Jimenez

Energy Project Manager.

GEPROP.

CHP concept. Contents: CHP definition. CHP options. Key steps in a typical CHP project. Reliability and Availability of a CHP system. Fuels and prime movers. CHP operating costs. Quotations on CHP usage. Concluding remarks.

Definition:

-Combined Heat and Power (CHP) is the on-site generation and use of heat and electricity in a cost-effective and environmentally responsible way.

CHP concept.

CHP technological options: -Gas turbine based scheme. -Steam turbine based scheme. (Rankine

cycle.) -Reciprocating engines. (Gas-fired or oil-fired

engines.) -Combined cycle. ...aiming at driving an electricity generator

and making practical use of heat.

CHP concept.

CHP concept.

VHP

IP

LP

Back pressure steam turbine.

Boiler

Feedwater

Fuel Electricity to process site and power grid.

Intermediate and low pressure steam to process site.

Schematic of a steam turbine based scheme

The overall efficiency of such systems can be in excess of 80% which leads to considerable reductions in emission of carbon dioxide, nitrogen oxides and sulphur oxides.

CHP:

-could boost your profit.

-increase your security of supply.

-improve your environmental performance.

CHP concept.

CHP concept.

The benefits of CHP

Environmetal. Strategic.

Financial.

More resources available for core business

Reduced NOx, SOx, CO2 emissions.

Cost savings.

CHP represents a major decision taken at board level.

Should be considered as an integral part of the overall company strategy.

It has a lifetime of up 25 years and its economics are typically evaluated over a ten year period.

It’s important to determine future demands and load profile because viability of scheme may be adversely affected by major reductions on heat and power loads.

CHP concept.

CHP concept.Raise awareness

Preliminary assessment

Board approval Draw up project spedification.Hold tender for full feasibility study

Commission full feasibility study, review results.

Board approval Develop full project specification.

Preliminary assessment NoYes

Feasibility study

No

YesIn house

3rd party

Appoint project team, develop plans and designs.

Place enquires for main plant, hold tender.

Finalise outline design, and financed package.

Board approvalShort list energy services and CHP suppliers, hold tenders.

Review tenders and negotiate terms.

Board approval

Review at later date

No

NoD

eta

ile

d d

es

ign.

Let contracts for supply.

Detail design, supply, instalation and comissioning.

Let contracts for supply.

Detail design, supply, instalation and comissioning.

Operation, maintenance and monitoring.

Su

pp

ly

Flowchart showing key steps in a typical CHP project process.

CHP concept.

Have all cost-effective energy efficiency alternative been considered?

Carry out a thorough energy review or audit of the site.

No

YesAre major changes expected to future heat and power loads?

Determine when future heat and power loads can be predicted.

Yes

Evaluate the likely future loads.No

Do the heat and power loads coincide?

CHP is unlikely to be cost-effective at present. Re-evaluate in the future.No

Does the anual operating period exceed 4500 hours/year?

Yes

Investigate the feasibility of CHP

Yes

No

Are you considering boiler up-grade, replacement or refurbishment?Yes No

START

Is a CHP an option for your company?

Energy demand profiles show the patterns of energy usage over specified time periods.

The success of the whole project depends on these profiles and it is essential that appropriate resources are allocated to producing these.

CHP concept.

CHP concept.E

lect

ricity

use

d, M

W

Hea

t lo

ad,

MW

Time. (hours. Time. (hours.)

Example: Site heat and power load profile.

00:00 00:0024:00 24:00

Reliability and Availability.

-These factors are really important. CHP system must operate over extended period of time in order to be economic.

-Reliability of a prime mover is a measure of its susceptibility to unscheduled shutdown.

-Availability take into account all outages and is a measure of its readiness to keep running.

CHP concept.

Reliability and Availability.

-Formulae for their estimation:

%Reliability = T – (S + U) x 100

T – S

%Availability = T – (S + U) x 100

T

CHP concept.

Reliability and Availability. (continue)

Where:

-S = scheduled maintenance shutdown. (hr)

-U = unscheduled shutdown. (hr)

-T = time period when the plant is available for service. (hr)

CHP concept.

Availability range.

-Gas turbine: 94 – 98 % have been achieved.

-Steam turbine: up to 99 %.

-Reciprocating engines: expect availability in the range 85 – 92 %

CHP concept.

Fuels.

-May be solid, liquid or gaseous and either “commercial” of waste.

-Commercial fuels: fossil fuel which are extracted and treated to varying degree and sold nation-wide.

-Waste fuels: are by-products of processing or domestic activities. Only economic if available locally.

CHP concept.

CHP concept.

Fuel Gross calorific value

Wood waste 15.8 MJ/kg

Heavy fuel oil 41.2 MJ/l

Gas oil 38.3 MJ/l

Natural gas 38.0 MJ/m3

Landfill gas 20.0 MJ/m3

Bagasse 10.5 MJ/kg

Prime mover.

-Mechanical machine which drives the electricity generator.

-Its correct selection is very important for successful instalation.

-Items such as: power output range, fuel to be used, the site heat:power ratio should be considered when choosing the best prime mover for the site.

CHP concept.

CHP concept.Type of plant. Typical output

range.Typical fuels. Typical

heat:power ratio.

Grade of heat output

Gas turbine 0.5 MWe upwards (over 200 MWe)

Natural gas, Gas oil, landfill, biogas.

1.5:1 to 3:1 High. (usually used in HRSG).

Compression engines

2 MWe upwards (till 15 MWe)

Natural gas + 5%gas oil, Heavy fuel oil.

1:1 to 1.5:1 Low

Spark engines Up to 4 MWe Natural gas, landfill, biogas.

1:1 to 1.7:1 Low

Steam turbine. 0.5 MWe upwards

Any but converted to steam.

3.1:1 to 10:1 Medium

Combined cycle

3.5 MWeAs gas turbine. Down to 1:1 Medium

Summary of prime movers.

Reciprocating engines: -Suitable for process sites having heat:power

ratio ranging 0.2 – 2.0 (max., economy ≈ 0.6) Gas turbine -Suitable for process sites having heat:power

ratio ranging 2.0 – 4.5 (max., economy ≈ 2.5 ) Steam turbine. -Suitable for process site having heat:power

ratio 4.5 upwards (max., economy ≈ 6.5)

CHP concept.

Suggestions for choosing CHP prime movers

CHP operating cost comprise:

-Fuel for the prime mover, and for supplementary and auxiliary firing if applicable.

-Maintenance, materials and labor including scheduled maintenance carry out by the manufacturers.

-Labour for operating and servicing the plant.

CHP concept.

CHP operating cost (continue):

-Consumables, e.g., lubricating oil, feedwater treatment chemicals, cooling tower dosing, as applicable.

-Other costs, e.g., insurance.

CHP concept.

Operating cost.

-Maintenance.

-Second biggest component of the operating cost of CHP after fuel purchases.

-Almost without exception will require the expertise of the equipment manufacturer or a specialist maintenance contractor for all but the most routine checks.

CHP concept.

CHP concept.

Prime mover

Typical operating and maintenance cost.

Reciprocating engine 0.0075 – 0.015 Euro/kWh

Gas turbine cycle. 0.0045 – 0.0105 Euro/kWh

Steam turbine cycle. 0.003 Euro/kWh

CHP concept. Item Annual site energy cost £ 000

. Existing. With CHP

Fuel A - existing boiler 2,034 1,550

Fuel B – gas turbine - 617

Total operating labour and maintenance.

250 308

Consumables and miscellaneous

80 88

Electricity purshased. 772 146

Electricity exported. (credit) - 258

Total energy running cost 3,136 2,451

Savings. 685

Summary of running cost for one installation.

Over 90% of the saving in running cost comes from the diference in electricity purshased.

The optimum CHP operating strategy, required to deliver the maximum cost benefits, will be strongly influenced by the electricity tariff structure.

Electricity tariff vary according to season and time of day.

CHP concept.

CHP is therefore optimised on the basis of only generating electricity when it is profitable to do so.

It is pointless to export electricity for a price less than it cost to produce.

CHP concept.

Factors favouring short payback periods:

-low investment cost.

-low fuel price.

-high electricity price.

-high annual operating hours.

-high overall thermal effciency.

CHP concept.

The following are quotations from Exxon Mobile when analysing its use of cogeneration............

CHP concept.

Exxon Mobile quotation which deserves some thinking........ A CHP facility cannot have external control of

its start-ups or shutdowns, nor outside control of cogeneration scheduling......

For a cogeneration project the electricity price is the most important variable in determining a project’s success—more so than capital costs, operating and maintenance costs and even fuel costs............

...it is critical to understand the market fundamental when deciding whether or not to export power into that market.......

....power market rules don’t typically recognise the inherent nature of cogeneration facilities and their tight integration within large manufacturing facilities.......

Exxon Mobile quotation which deserves some thinking........

Concluding remarks. Economic viability of CHP system largely

depends on: -price structure of fuel and electricity. -running hours of the site. When choosing the CHP system which best

suit the total site needs there should be considered:

CHP concept.

-Heat:power ratio and its annual variance.

-Power tariff structure.

-Power Load factor demand and its annual variance.

CHP concept.