The difference between LCV and HCV (or Lower and Higher Heating Value, or Net and Gross) is clearly understood by all energy engineers. There is no 'right' or 'wrong' definition.
Perhaps I could comment as someone with direct experience as a project leader in gas turbine power generation/CHP technology.
The difference between LCV and HCV (or Lower and Higher Heating Value, or Net and Gross) is clearly understood by all energy engineers. There is no ‘right’ or ‘wrong’ definition. The numerical difference between the two is the latent heat of condensation of the water vapour in the combustion exhaust gas, which in turn depends on the hydrogen content of the fuel being burned.The difference is minimal for coal, significant for natural gas and largest for pure hydrogen fuel. So you have to do the conversion calculation for the specific case. Unfortunately, for historical reasons, the natural gas (public supply) and coal industry (inc’ coal-fired power stations) have grown up using HCV, while engines (all fuels, inc’ diesel) and gas turbines have ended up using LCV basis, giving slightly higher nominal % efficiencies for those products. This is not about ‘salesmen and spin’, it’s just engineers using different bases.
The commercial availability of CCGT ‘pure power’ (i.e. non -CHP) plant with 60% LCV basis efficiency is quite genuine and commercial, not just ‘in the laboratory’. This is the GE ‘high-tech’ steam-cooled H Class turbine, see http://www.gepower.com/prod_serv/products/gas_turbines_cc/en/h_system/index.htm The first H Class System located at BP Baglan Bay refinery in Wales has been in commercial operation since September 2003 and has achieved significant operating experience. Siemens and Mitsubishi MHI are also both on the point of introducing 60% LCV systems. However, a more common ‘state of the art’ for the new-build market today is 58% LCV efficiency. The overall gas CCGT ‘fleet average’ is probably c.53%. The chosen % LCV efficiency for any project is a function of fuel cost as there is a trade-off between efficiency and capital cost, so some low fuel cost areas e.g. Middle East are still buying 52% LCV efficiency today. before any one asks, there would be no point in fitting condensing heat recovery on to a CCGT plant to ‘increase’ its efficiency. Because of practical thermal cycle limits (so-called ‘temperature pinch’), it would not increase the overall efficiency (-which is why it’s not done!). CHP is different, see below. CCGT efficiency will rise further in future, but there is a ‘law of diminishing returns’ and I’m not expecting to see 70% (LCV). For all engine and turbine-based plant there are part-load efficiency losses, and also power output losses at higher ambient air temps. The amount of the loss is specific to the machine – you have to consult manufacturers’ literature. CHP (Combined Heat & Power), as constantly recommended for all fossil-fuel plant by Claverton, is quite another matter. It is easy to achieve 80-90% on HCV (=85-95% LCV on gas) even with a relatively low efficiency prime-mover (GT or engine), even at quite a small scale. The efficiency is controlled by the final ‘cold-end’ (pre-chimney) heat recovery, not by the prime mover. One effect of this is that CHP plant have almost no part-load efficiency loss, in fact in some cases it tends to increase.In CHP, the effect of prime-mover efficiency is to change the proportions (ratio) of heat and power produced (assuming that the customer can use both) – lower PM nominal efficiency = more heat. It is perfectly possible to use condensing heat recovery on large scale CHP plant (especially with clean gas fuel) and get efficiency up to 95% HCV basis, just as with a domestic gas boiler. My colleagues in British Gas were field-demonstrating such systems back in 1985. For reasons which escape me, it is not common practice in the industrial CHP market yet – it should be. Gregor: large slow-speed diesel engines of at least 10MW size (e.g. as used to power container ships, or grid power plants) have efficiencies up to about 50% LCV, or 55% with the exhaust heat recovery you refer to – eg see http://www.dresser-rand.com/steam/pdfs/85218_MarineST_A4sm.pdf . Unit sizes are now available up to 50 MW. But the higher speed diesels used for smaller duties (e.g. on-site gen sets) are significantly less efficient, down to 35% LCV. Regards all, Chris Hodrien Expansion Energy Ltd
—– Original Message —– From:
Sent: Wednesday, January 06, 2010 11:37 AM Subject: Re: [Gridsupergridetc] Fwd: [BBC Radio4] Efficiency of CCGTs
Do you know the difference between LCV and HVV? It is simply the condensation energy of the steam in the exhaust gas. This can at standard conditions only be gained at a theoretical maximum of 100°C. This part of the energy is not at all sufficient for a high performance power generation. Just check what efficiencies you can gain from a low temperature power plant at 100°C. So I would not harp on about the higher heat value.
From: Dr. Gregor Czisch
Sent: 06 January 2010 11:21
There are Combined Cycle power plants with efficiencies above 58% (ISO conditions).
Fortschrittliche Gas- und Dampfturbinenprozesse zur Wirkungsgrad- und Leistungssteigerung bei GUD-Kraftwerken
Dipl.-Ing. C. Kail, Dr.-Ing. B. Rukes VDI, Erlangen
New power plants with efficiencies above 60% have been announced almost 5 years ago
Siemens baut und betreibt neues GuD-Kraftwerk für E.ON auf eigenes Risiko
I did not check if they are built now. But it seems as if one would be ready this year and 58% of efficiency was reached by Siemens in 2001.
See Seite 6 (Page 6 (7 in the acrobat counter)) “Entwicklung der Gasturbinen-Technologie” in
Efficiency by the Numbers
PS: I have heard that it is planned to build big diesel engine power power plants with an extra steam process feed by the exhaust gas of the engine. This combination should reach about the same efficiencies as classical combined cycles. Does anybody know about a realised one?
Am 05.01.2010 20:20, schrieb starrfred
Dear David O
Dear David Oliver
The CEGB switched over to quoting efficiency values in terms of the net CV around 1985. This seemed to be in line with world wide policy at that time, although the American DOE wants things in terms of gross CV.
The argument for quoting the net figure are the impossibility with most energy conversion systems of recovering the latent heat in the water of combustion.
Your point about part load efficiencies is not as well founded as you may think . Part load efficiencies are rarely quoted……In particular CHP organisations are silent on this vital matter.
It is perhaps doubtful that the Frame H machine does heut 60% net efficiency, but I would bet that existing machines run at more than 58%.
I would expect that CCGTs will eventually surpass the 70% net level ( 63% gross) , if engineers were willing to accept more complex gas turbines
Fred Starr .
———- Forwarded message ———-
From: David Olivier <
Dear Mr Murcott
I am sorry to demur but CCGT power plants are not 60% efficient in
converting gas to electricity unless this refers to an experimental plant
and refers to the lower calorific value (LCV) basis. Commercial CCGT plants
are just under 50% efficient, as a weighted average, on the higher calorific
value (HCV) basis.
The UK until recently tended to quote figures where possible on the HCV
basis since this avoids seriously misleading people. For instance, gas
condensing boilers are up to about 95% efficient, etc. If the LCV is
adopted, one gets all manner of figures which seriously confuse lay people,
such as boilers with an efficiency of 105 or 107%. It does seem that
salesmen for CCGT plants have in recent years resorted to LCV solely to make
their figures look better.
As I said, Dr Riley might like to contact the Claverton Energy Group forum
where a number of power engineers can probably enlighten him further as to
the losses from part load operation – which all power stations, apart
principally from the nuclear plants, have to do. I understand that these
reduce the actual average efficiency in use to under 50%, although CHP might
with some effort extract another 40%.
In short, neither the 70% figure nor his new 60% figure is correct and both
tend to mislead.
David Olivier BSc MASHRAE
ENERGY ADVISORY ASSOCIATES
1 Moores Cottages, Bircher
Leominster, Herefordshire, UK, HR6 0AX
From: Toby Murcott
Dear Mr Olivier
Thank you for your email to Home Planet regarding the efficiency of gas
power stations. I am sorry that you felt your enjoyment of the programme was
marred by incorrect facts, we do strive hard to make sure that the
information within the programme is correct.
The person who made the comment on gas power station efficiency was Dr Nick
Riley, Head of Science Policy (Europe) at the British Geological Survey,
President of CO2GeoNet and member of the UK Government’s Advisory Committee
on Carbon Abatement Technologies. I forwarded your email to him and he has
replied that “Modern Combined Cycle Gas Turbines are 60% efficient. CCGT
with combined Heat & Power up to 89%.”
He further adds:
“The question being dealt with in the programme was actually about nuclear
generation efficiency. The efficiency advantage that gas has over nuclear
and coal is that you can combine two different generation methods with gas
into one combined system. The first is combustion of the gas to drive a
turbine (which is essentially a jet engine) and then use the combustion
heat exhaust to create steam that can then be sent through the steam cycle
turbines to generate yet more power. Coal and nuclear are limited to the
steam cycle only, which limits their power generation efficiency.”
He also attached two documents which I have forwarded with this email.
Thank you again for your email and I do hope that this clarifies the
comments made on the programme.
With best wishes
Producer, Home Planet