Going the whole hog on CHP
02-MAY-2006
biogas from Czech pig farm fuels cogen units
A large pig farm in the Czech Republic
is currently operating its second CHP installation fuelled by biogas produced
from farm slurry. Here, Vlado Murár and Radomír Řeháček
describe the use of biogas in CHP plants and the installation at the pig farm,
which is getting a return on investment by selling electricity to the grid.
Combined electricity and heat production is making headway into the use of
renewable energy resources. Small cogeneration units increasingly use renewable
fuels in what were traditionally fossil-fuel-fired applications. Waste treatment
gas, landfill gas or biogas – examples of renewable fuels – are used by cogeneration
plants based on combustion engines at sewage treatment works, municipal waste
sites and agricultural sites. Many countries support the use of these alternative,
renewable fuels in energy production by providing investment grants or advantageous
purchase prices for renewable electricity. This is why the ‘green cogeneration’
market is beginning to show promising development.
Biomass – produced during anaerobic breakdown of biological material such as
farm animals’ excrement or vegetable biomass – is especially attracting interest
as it is a fully renewable energy source.
CHP units serve a pig farm at Velké Albrechtice in
the Czech Republic. Biogas is considered a form of renewable energy in many
countries
BIOGAS FOR ENERGY PRODUCTION
In terms of energy potential, biogas is similar to natural gas, the most commonly
used fuel for cogeneration units. However, the sulphur content of biogas requires
specific modifications to be made to the cogeneration equipment. Sulphur compounds
can cause formation of acids (and thus corrosion) on inlet and flue gas tracts,
oxidation/burning of spark-plug electrodes, and faster decomposition of lubrication
oil. Modifications of CHP units therefore consist mainly of using more resistant
materials for inlet and flue gas pipes, using more suitable materials (such
as materials with minimum copper content) for the engine’s slide bearings, using
lubrication oils with higher alkalinity, and adapting the frequencies of spark-plug
and oil changes.
The large volume of biogas extracted and its generally low pressure when entering
the engine makes it imperative to properly design the gas extraction and supply
system. Adjustments consist of increasing the dimensions for tubings and fittings
(such as electromagnetic ventilators and gas pressure regulators) and installing
equipment to regulate the gas mixture’s composition and quality.
Biogas has been used for energy production for many years in the Czech Republic.
Its development and use has been accelerating considerably since 2002, when
new biomass electricity purchase prices were introduced. Before then, operators
had used the cogenerated electricity and heat mostly for their own needs, because
electricity sale to public grids was not very profitable. With the new purchase
prices of about €90/MWh, it quickly became profitable to use the biogas
for combined electricity and heat production and for power export.
Previous biogas experience gives a clear advantage and the biogas station at
a pig farm in Velké Albrechtice in eastern Czech Republic is an example.
The pig farm’s old digester
PIG FARM SLURRY DISPOSAL
The large pig farm in Velké Albrechtice started operation in 1974. Farm slurry
was treated and disposed of using aerobic mechanical and biological processes.
After years of operation, the treatment technology wore out and was replaced.
Despite the retrofit, the operation of the treatment plant was still unsatisfactory,
so the farm considered other ways of treating the slurry.
In 1989 plans for building a biogas cogeneration station started, and the station
began operation in May 1995. Biogas was pumped by a blower from a gas collector
to the energy centre with four 140 kW CKD Horovice gas engine cogeneration units.
Despite the low reliability of the cogeneration units – which were first installed
as dieselpowered units in 1990 and underwent adjustments for biogas combustion
– during the first six years of operation they produced over 4 million kWh of
electricity, and the waste heat produced was used for heating the digesters
and warming up part of the pig sty. However, in winter 2001, the CHP units were
so worn out that they could not be used anymore.
The pig farm’s new digesters processes 140 m3
of slurry daily
The biogas station operator then started looking for another CHP manufacturer
and eventually chose the company Tedom. But the project faced financial problems.
The company owning the pig farm, GT 92 s.r.o., was unable to invest in CHP units
with its own resources. It met with various banks, but its loan applications
were unsuccessful. Prospects of buying a CHP unit through leasing companies
similarly ended in frustration. As of July 2001, 2500 m3 of biogas
was still being burned off per day and GT 92 s.r.o. was – despite the project’s
solid economic return of investment – unable to secure financing for the purchase
of a new CHP unit. Tedom helped to solve the situation with its own leasing
offer, and a leasing contract was signed in July 2001. From then on, things
started to take off. In a short time, a TEDOM Cento 140 SP cogen unit (based
on a 140 kW engine) was manufactured, transferred to GT 92 s.r.o., installed
and, in November 2001, started operation (see ‘View from the equipment supplier’
on pages 68–69).
View from the equipment supplier
To get the view from the side of the cogeneration technology supplier,
we asked Tedom’s Inland Sales Director, Libor Talasa, some questions.
What problems did you face when installing the first cogeneration
units in the pig farm?
The initial problem lay mainly in trying to persuade the investor to install
new CHP units because it had had a poor experience with CHP reliability.
By that time we already had several CHP units installed in sewage treatment
plants; therefore we invited the investor’s representative to visit one
such installation in Chrudim, where the same CHP unit with 140 kW of electrical
output operated. After consulting with the operator and inspecting the
installation, the investor’s initial distrust was reduced. The investor
was mainly attracted to the unit’s annual running time of 8000 hours and
the 41,000 total operating hours by the time of the visit.
The next problem was in persuading the investor to upgrade the whole
installation. Originally it wanted to change just the old, defunct engine
for a new one, together with some worn-out peripheral parts. After a series
of discussions, the investor understood that the purchase of new units
would be more beneficial.
How did you deal with the high sulphur content in the biogas?
We entered this project with the awareness of the fuel’s low quality.
Therefore we created a team of developers to analyse the potential risks
related to the low-quality gas and to suggest effective measures. This
installation used a newly developed cogeneration unit specially adapted
to low-quality fuels. This unit also operates under close monitoring:
oil samples were taken and analysed after 200 operating hours and the
data were used to set service intervals.
Biogas digester at Klokocov
Is the hire-purchase sale a standard method of selling cogen units?
Hire-purchase sale isn’t a standard method of selling cogeneration units,
but every company must be ready for it. Here, it was necessary to know
the purchaser well and to try to minimize financial risks connected to
the sale. You must also trust the product you’re selling. If customers
aren’t satisfied with the product quality, they can rightfully stop paying
and we can only take the worn-out device back.
Currently, another biogas station in Klokocov, some kilometres from
Velké Albrechtice, is getting ready to start. In what ways will it differ
from the two previous ones?
The biogas station in Klokocov is being built to process plant and organic
materials together with cattle and porcine slurry. The two biomass reactors
measure 2500 m3 each and the technology is similar to the new
biogas station in Velké Albrechtice. The main difference is in the choice
of cogeneration units. On the one hand, the station wanted a bigger CHP
unit because of the huge stable quantity of biogas; on the other hand,
it wanted to minimize the risk of engine failure and losing sales to the
grid by relying on two large units in case one unit fails. Therefore we
recommended a combination of three 140 kW Tedom units and one 520 kW Deutz
engine unit. We believe that the Deutz engine will be good and will be
as reliable as the Tedom engines used so far.
What’s your current view of the future of biogas cogeneration?
I think that the future of using biogas for combined electricity and heat
production will be very good because it is supported by the state in many
countries and makes profit for its operators. The greater demand for cogeneration
units also shows a rising investment interest.
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TRIAL YEAR FOR THE COGEN PLANT
The first year of operation was a trial year. As the pig farm already had many
years of experience with operating CHP units, it was unclear how the new units
would deal with an unpurified raw biogas with a large sulphur content.
However, thanks to the high-quality stainless-steel design, the new units worked
well, and after a year’s successful operation, the company purchased and installed
two more units with the same output.
In 2003, the production of biogas increased, and another CHP unit was added.
With two more units installed in 2004, the pig farm now has six 140 kW engines
with a total electrical output of 840 kW.
The biogas station consists of two digesters, a gas collector, an energy centre
and storage wells for the processed slurry. Each digester, made of steel plates,
has 2500 m3 of capacity. The processed slurry is transferred to storage
wells with 5000 m3 capacity, after which the slurry can be used immediately
as manure to treat fields, or stored in a 15,000 m3 disposal site
2.5 km away in the fields, for further use as manure .
Part of the waste heat from the CHP units were used
for heat the digester
The biogas station processes 140 m3 of raw slurry with 6% solids
daily. Approximately 28 tonnes of other organic matter is added to this slurry.
Organic matter consists of meat-bone powder and waste sludge from a nearby wood-pulp
factory. Over 7000 m3 of biogas is produced per day.The biogas contains
about 65% methane and around 1500 mg/m3 sulphur compounds. Monthly
electricity production ranges from 400 to 430 MWh and there are plans to increase
it to 500 MWh in the second half of 2006.
All the electricity is sold to the grid at the current price of €92/MWh.
The pig farm uses 82% of the heat produced by the CHP units to heat the biogas
reactors, to produce hot, sanitary water, to heat the delivery site for up to
480 suckling pigs (via underground heating which replaced the original electrical
heating), and to dry farm crops with a hot-air drier with 300 kW of power output.
The biogas station’s return on investment is estimated to be 6–7 years at current
electricity purchase prices.
Currently a new biogas station is being built next to the existing biogas station
at Velké Albrechtice. Planning for this new station draws from the experience
with the existing one. The reactor design is different. It is made of concrete,
with an integrated plastic gas collector and horizontal propeller stirrers.
The feed material intake is also newly designed, which allows the slurry mixture
to be pasteurized daily. Total electrical output of the new Tedom cogeneration
units will be 900 kW.
Vlado Murár works with TEDOM s.r.o., Výcapy, and
Radomír Řeháček is the power engineer at GT 92 s.r.o., Velké Albrechtice,
the Czech Republic.
e-mail: murar@tedom.cz
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