5. Sizing and installation of cogenerators powered by biogas

AD-NETT
Technical summary
BIOGAS USE IN PIG BREEDING:
SIZING AND INSTALLATION OF COGENERATORS IN ITALY(*)
Sergio Piccinini(1,2), Claudio Fabbri(1), Giovanni Riva(3)
(1) Centro Ricerche Produzioni Animali - CRPA
C.so Garibaldi, 42 - 42100 Reggio Emilia - ITALY
Tel. +39-0522-436999 - Fax +39-0522-435142
E-Mail: [email protected]
(2) Member of Italian Biomass Association (ITABIA)
Via C.Colombo, 185 - 00147 Roma- ITALY
Tel. +39-06-5122792 - Fax +39-06-51601202
E-Mail: [email protected]
(3) Ingegneria Agraria, DIBIAGA, Università di Ancona
Via Brecce Bianche - 60131 Ancona - ITALY
Tel. +39-71-2204854 - Fax +39-71-2204858
E-Mail: [email protected]
(*)
Extracted from the handbook “Biogas e Cogenerazione nell’allevamento suinicolo”
(Biogas and cogeneration in pig breeding), chapter 5, edited by CRPA and ENEL, October,
1996.
CONTENTS
1. CHARACTERISTICS AND PERFORMANCE OF SMALL CHP PLANTS ............................3
1.1 Market availability......................................................................................................................3
1.2 General analysis of performance and main characteristics ....................................................4
1.3 Technical analysis of the most suitable models for the livestock production sector.............8
1.4 Conclusions ................................................................................................................................17
2. SIZING AND INSTALLATION OF ENDOTHERMIC COGENERATORS...........................18
2.1 Biogas production and sizing of the cogenerator ...................................................................19
2.2 Economic analysis of the system ..............................................................................................19
2.3 General recommendations........................................................................................................23
3. REFERENCES ................................................................................................................................25
2
1. CHARACTERISTICS AND PERFORMANCE OF SMALL CHP PLANTS
This paper analyzes the combined heat and power (CHP) plant market to obtain some general
indications that may be useful for defining the state of the art of this sector.
Considering that the average size of livestock farms rarely allows installing electrical power
greater than 80-100 kW (the most likely power is 15-25 kW, depending on how the energy
produced is managed), the market analysis examines otto cycle gas engines and is limited to
electrical power of less than 100 kW.
Machines with diesel cycle engines are not considered, as in order to use the biogas, the dualfuel versions must be used, which are obtained from the transformation of standard engines
carried out by the few specialists in the sector. The user would thus be in the condition of
ordering an "out of catalogue" machine having technical characteristics that are generally
unknown, excepting the maximum power that can be produced.
1.1 Market availability
Historically, CHP plants based on reciprocating engines have never constituted a product type
per se, as they are basically an improved version of generating sets in terms of energy
efficiency. This is also true in terms of the traditional purchasers, who are generally
technicians interested in generating electricity with machines of a size which is almost always
greater than 150-200 kW, for which the technological implications of the problem are clear
and, consequently also the question of whether or not it is suitable to recover energy and
create part of the system oneself.
It should also be emphasised that by finding the single components (engine, heat exchangers,
electrical devices, etc.) on the market, even a small workshop is capable of offering a vast line
of machines.
The more limited power levels, on the other hand, require a commercial approach similar to
that used for small-medium water heaters or refrigerating units; i.e. high modularization (thus
heavy investments for product development), and the availability of sales and service
networks. These prerequisites are certainly not within the capacity of the generic producer of
generating sets, particularly due to the commercial and economic restrictions.
In fact, the few existing gensets offered in this sector, considered below, come from large
industrial firms.
The world leader of this type is certainly the TOTEM line (created by the FIAT group),
composed of machines with very interesting characteristics (analyzed below) and still present
on the market today.
Alongside this line, we should consider the evolution of the small generating sets (20-90 kW)
created to satisfy the typical needs of rural settlements on the islands of northern Europe and
3
now also presented in the cogenerating version, sound-proofed and including all the necessary
regulation. Substantially, a modular structure is proposed, including acoustic insulation and
all the elements necessary for operation, requiring only the electrical and hydraulic
connections.
The right combination between the power of the module and the user’s energy requirements is
accomplished with a suitable number of units connected in parallel.
The use of an reciprocating engine, however, requires a somewhat intense maintenance
schedule. As a result, the installers typically propose a special service contract based on the
number of operating hours of the machine. At first glance, these contracts could seem to be
financial burden, but in the long run they can be advantageous, because they avoid removing
the user from normal farm management.
Due to the lack of real incentives, the CHP plants market in general, and with particular
reference to the agricultural context, has always been difficult and characterized by low
numbers.
In the Italian rural setting, it is estimated that no more than 150-200 units are in operation, a
large part of which are composed of TOTEM modules (in systems that include 1-4 machines).
Within this yet limited diffusion, a fundamental role has been played by the incentives for
energy savings (e.g. Italian Law 308/82 and 10/91) which have always been interesting for the
agricultural sector (up to a 60% contribution on investments without security). Also part of
this scenario is a provision of the Italian government of 1992 that offers incentives for selfproduction of electric energy from biomasses, paying about 270 ITL•kWh-1 (0.14
EURO•kWh1) against an average cost of 160-180 ITL•kWh-1 (0.08-0.09 EURO•kWh-1). This
could translate into renewed interest in biogas systems for animal breeding. However, this
rule is stopped from July 1996 and today is under revision. Italian Programme for Renewable
Energy from Biomass is part of the Italian politics for reduction of greenhouse gases
emissions, according to Kyoto Protocol. Specific laws and decrees will better define the
amount of financial support to be distributed.
1.2 General analysis of performance and main characteristics
Table 1 summarizes the main characteristics of the machines sold by 9 firms (all operating in
Italy) which represent a more than significant sample of the current offer on the market.
These machines are otto cycle cogenerators with electric power that ranges, in round figures,
from 14 to 3,200 kW, all suitable to operate with LPG, natural gas, and biogas.
An in-depth analysis of the machines currently offered on the market shows that:
4
Table 1 - General characteristics of the main otto cycle cogenerators sold in Italy (minimum and maximum values).
Manufacturer
Distributor
Power
Rendimento
IEN
intake
mechanical
electric
thermal
mechanical
electric
thermal
total
(kW)
(kW)
(kW)
(kW)
(%)
(%)
(%)
(%)
Continental
Energy System
Savener
74-289
22-95
20-90
50-170
30-33
27-31
58-67
89-95
0.76-0.81
Alcatel
Alcatel
432-2,520
146-1,009
132-908
220-1,150
32-43
29-39
41-56
74-89
0.62-0.83
Tessari
Tessari
147-1,094
39-333
35-300
80-610
27-32
24-29
52-57
80-83
0.61-0.67
Ing. Mattei
Ing. Mattei
502-2,451
166-840
154-802
290-1,210
32-37
30-34
45-58
75-88
0.60-0.78
FIAT
Tem
56
14.8-16.7
13.3-15
39
27-30
24-27
69
93-96
0.74-0.80
Deutz/MVM
Intergen/Topgen
518-2,858
168-1,000
160-884
297-1,602
32-35
30-34
56-60
88-90
0.75-0.79
Jenbacher Werke Jenbacher
Energiesysteme
772-3,829
291-1,467
279-1,420
399-1,932
37-41
35-39
49-53
87-89
0.79-0.83
Caterpillar
C.G.T
278-2,892
95-1,011
85-960
150-1,432
32-37
29-34
46-55
76-88
0.61-0.77
Ulstein Bergen
TecnoEnergia
41-41
39-40
50-52
90-92
0.85-0.86
2,550-7,660 1,053-3,157 1,000-3,030 1,743-3,990
5
- the electrical and mechanical efficiency (Figure 1) increases along with the increase in the
size of the machine. With reference to the former (electrical efficiency, which is of greater
interest on the practical level), the minimum values (corresponding to 15 kW machines) are
in the vicinity of 23%, while the maximum values (obtainable starting from 400-500 kW)
reach 40%. Certain machines, however, surpass 30% with power levels on the order of 90
kW. Above 1,000 kW it can be noted that there is a "quality leap" and all the cogenerators
surpass 36%. This is a widely predictable result, as the more powerful machines in general
involve more accurate design and manufacture and, therefore, are more efficient than those
of lesser power which are normally designed to keep production costs low -
40
Electrical efficiency (%)
38
36
34
32
30
28
26
24
22
20
0
200
400
600
800
1000
1200
1400
1600
Net electrical power (kW)
Figure 1 - Electrical performance of the main otto cycle cogenerators sold in Italy.
the thermal efficiency (Figure 2) is almost inversely proportional to the size of the
cogenerator, ranging from a minimum of 40% to maximum values nearing 70%. The most
frequent values are between 52 and 58%. In general, on the smaller machines of a more
traditional design, the heat of the exhaust gas and the engine is recovered, while the larger
machines also use the heat obtained from lubricating oil cooling. In the small modular units,
on the other hand, heat recovery is always high (the technological vertex is accomplished by
the TOTEM system, where the alternator is cooled as well), and reaches greater values
(70%). The thermal energy is supplied in the form of hot water at temperatures between 80
and 90°C. In practice, the systems almost always operate at temperatures between 75 and
85°C, while at 95°C the alarm procedures are activated. In the modular units, all the
exchangers are connected by a primary circuit and the heat is transferred to the user with a
6
plate-type water-water exchanger. In other types, the user must create the layout by
connecting the various exchangers according to needs. The only closed circuit made in the
factory, then, is that of the engine block which normally dissipates the energy through a
plate-type exchanger (in place of the classic radiator). This makes it possible, for example,
to produce water steam with only the exhaust gas (thanks to the high temperature available,
which is always greater than 500°C in maximum load conditions) and hot water at 80°C
with the remaining exchangers. The exchanger with most variable constructive
characteristics is the one operating on the gas, ranging from elements in cast aluminium, to
classic swabbable pipe bundles made of steel (normal or stainless) obtained by means of
welded elements and beading of the pipes, to "monopipes" in steel (formed by two
concentric tubular elements). The most widely used solution is that of the pipe bundle;
70
Thermal efficiency (%)
65
60
55
50
45
40
35
0
200
400
600
800
1000
1200
1400
1600
Net electrical power (kW)
Figure 2 - Thermal performance of the main otto cycle cogenerators sold in Italy.
- the total efficiency ranges from 80 to 90%, and the small modular units are the most
efficient of all (94-96%). This is thanks to two concurrent factors: their high thermal
efficiency, and the greater weight, in terms of total efficiency calculation, of heat recovery
with respect to electrical energy production.
For the electrical connections, there are basically two more widely used layouts:
- machine operating in "stand-alone" mode with self-excited generator and starter motor
connected to batteries, typically used for the contracts of transfer of excess electrical energy
to ENEL (the Italian electric utility). A switching board joins the user to the public mains or
7
to the generator alternatively. This is the classic configuration of the emergency generating
set, which is often preferred because of the limited investment required (limited to the
electrical system). Nonetheless, this configuration makes it necessary to oversize the
cogenerator, which must also be able to handle the starting peaks of the electric motors
present on the user network; during startup, it does not supply the user for a few seconds,
making it necessary to install uninterrupted power supplies where electronic control circuits
are in operation, or in any case equipment that cannot be switched off; it requires a control
that switches off the cogenerator and switches to the public mains in the event that the
power absorbed by the user is too low for prolonged periods (a fact which leads to rapid
fouling of the engine and high specific consumption levels). This solution, therefore, is
suitable for uses that are particularly simple in distributive organization and free of electric
motors with power greater than 25-30% that of the cogenerator;
- machine connected to the public network from which it absorbs magnetizing energy, typical
of the contracts of transfer of all the electrical energy produced to ENEL. This is the
simplest parallel configuration. The engine operates at constant power (the respective
controls, then, are simplified); there are no longer problems of peak absorption; the machine
is started with the generator. On the other hand, the cogenerator stops if the mains voltage is
cut off. The controls on the energy produced (except for the related metering) are reduced to
the verification of the stability of the electrical measurements (voltage and frequency), in
order to prevent prolonged conditions of anomalous operation. In the past, this solution was
mainly unsuccessful for two reasons: users' preference for machines able to operate also in
black-out conditions, and the low price of the energy delivered to the grid.
The system solutions that enable both parallel operation and "stand-alone" operation, on the
other hand, are little used due to the investments required for the interface equipment.
1.3 Technical analysis of the most suitable models for the livestock production sector
The power levels of practical interest to farms are on average lower, indicatively, than 100
kW with peaks (reserved to particularly large farms) that may reach 200-250 kW.
These limits derive from two basic considerations:
- the energy consumption of the livestock farms, in the end, is limited and does not require
high power demands;
- though in consideration of maximizing the advantages offered by Italian Law (possibility to
sell to the network the produced energy at 270 ITL/kWh (0.14 EURO/kWh), the size of the
machines is limited by the availability of fuel.
In terms of application, biogas must not be confused with a simple mixture of methane and
carbon dioxide. The potential problematic factors for utilization in engines are the following:
8
- water vapour: damaging not so much during operation as with the engine stopped. Any
condensates formed, in fact, absorb the corrosive sulphur and ammonia based elements
contained in the gas itself and, subsequently, attack all the surfaces on which they are
deposited (e.g. exchanger operating on the exhaust gasses, cylinder combustion chambers,
pipelines, etc.), as well as polluting the lubricant. The problem thus becomes more serious
the more the machine is subject to cycles of switch-on and switch-off. To reduce this
problem, solutions are adopted that foster the formation of condensate before the gas
reaches the engine, such as: collection well placed along the piping which normally
separates the cogenerator from the gas production point (usually at least 50-100 m), a small
intermediate gas-meter, or a small cooling system. In addition, these solutions provide the
beneficial result of eliminating a good part of the other pollutants. In other cases, it is
preferable to install units with a timed system which, before the machine stops or the gas
finishes, supplies the unit with another fuel (natural gas or LPG) for about one minute;
- sulphur-based compounds: these are always dangerous because they attack the copper
contained in the bearings and in the engine valve guides, and the consequences are always
serious. Traditionally, desulphurizers are used which, given the moderate dimensions of the
systems, must be extremely simple to limit the costs. This leaves little room to solutions that
are efficient and, above all, ensure sufficiently constant performance over time. In fact, a
bed of iron filings is almost always proposed; nonetheless, the most suitable method seems
to be that of acting beforehand by avoiding copper-based engine components (e.g. using
bearings in white metal), using lubricants with a high TBN (parameter proportional to the
ability to absorb and neutralize foreign substances) and renouncing any purification
intervention;
- particulates: constituted of all the elements, both organic and inorganic, that are drawn along
by the gas. They do not represent a particular problem if the water vapour is removed
effectively;
- variability of the methane content: this influences the carburation of the machine, and thus
the regularity of work;
- variability of pressure (always generated by the incongruency between gas consumption and
gas availability): the problem is resolved by permitting cogenerator operation when the
manometric values are maintained within the tolerance limits. In practice, this only regards
the idling, as excessive pressures can be easily controlled with a suitable reduction unit.
Summing up, cogenerators destined for farm use should be reduced in size and suitable to the
chemical-physical characteristics of the biogas which, as we have seen, leads to a series of
operating solutions. Tables 2 and 3 summarize the principal characteristics of a number of
cogenerator models with electrical power less than 100 kW.
9
Table 2 - General characteristics of the otto cycle cogenerators with electrical power less than 100 kW sold in Italy.
Prog.
no.
ManufacturerAssembler
1
Continental
Energy System
“
“
“
“
Tessari
“
“
“
“
“
“
“
FIAT
“
“
“
“
“
“
“
“
Caterpillar
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
Cogenerator
Distributor
Savener
“
“
“
“
Tessari
“
“
“
“
“
“
“
Tem
“
“
“
“
“
“
“
“
C.G.T.
Engine
Manufacturer Type/Model Mechanical Engine
power
efficiency
(kW)
(%)
Bibloc BB20A
Continental Teledyne TM
22
30
Energy System
27
Bibloc BB30A
Valmet
420 G
33
30
Bibloc BB60A
Valmet
612 G
64
32
Bibloc BB90A
Valmet
612 GSJ
95
32
Bibloc BB90AS
Scania
DN 11
95
33
n.d.
Iveco Aifo
8,061 G
44
30
n.d.
Iveco Aifo
8,061 G
39
27
n.d.
Iveco Aifo
8,361 G
67
30
n.d.
Iveco Aifo
8,361 G
61
28
n.d.
Iveco Aifo
8,361 SG
89
31
n.d.
Iveco Aifo
8,361 SG
80
28
n.d.
Iveco Aifo
8,210 G
111
30
n.d.
Iveco Aifo
8,210 G
106
29
TOTEM standard
FIAT
127A
17
30
TOTEM standard
FIAT
127A
17
30
TOTEM standard
FIAT
127A
15
27
TOTEM indipendente
FIAT
127A
16
29
TOTEM indipendente
FIAT
127A
16
29
TOTEM indipendente
FIAT
127A
15
26
TOTEM stand-by
FIAT
127A
16
29
TOTEM stand-by
FIAT
127A
16
29
TOTEM stand-by
FIAT
127A
15
26
n.d.
Caterpillar
3,306 NA
95
34
Type/Model
Power
supply
Type of
No. Displacement
fuel
cylinders
(cm3)
A
M
4
2,680
A
A
SI
A
A
A
A
A
S
S
A
A
A
A
A
A
A
A
A
A
A
A
M
M
M
M
M
B
M
B
M
B
M
B
M
P
B
M
P
B
M
P
B
M
4
6
6
n.d.
6
6
6
6
6
6
6
6
4
4
4
4
4
4
4
4
4
6
4,400
7,400
7,400
n.d.
5,900
5,900
8,100
8,100
8,100
8,100
13,800
13,800
903
903
903
903
903
903
903
903
903
n.d.
A = Induction; S = Supercharged; I = Intercooler;
M = Methane (CH4>80%); P = Liquid petroleum gas; B = Biogas (CH4 = 65%); G = gas oil.
10
Table 3 - Performance of the otto cycle cogenerators with electrical power less than 100 kW sold in Italy.
Prog.
Power
Efficiency
no.
intake
(kW)
mechanical
(kW)
electric
(kW)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
74
111
201
293
289
149
147
221
217
288
288
365
365
56
56
56
56
56
56
56
56
56
278
22
33
64
95
95
44
39
67
61
89
80
111
106
17
17
15
16
16
15
16
16
15
95
20
30
60
90
90
40
35
60
55
80
72
100
95
15
15
14
15
15
13
15
15
13
85
thermal Mechanica
(kW)
l
(%)
50
30
75
30
130
32
170
32
170
33
80
30
84
27
120
30
120
28
158
31
158
28
200
30
200
29
39
30
39
30
39
27
39
29
39
29
39
26
39
29
39
29
39
26
150
34
Other characteristics
Electric
(%)
thermal
(%)
total
(%)
lenght
(cm)
width
(cm)
height
(cm)
mass
(kg)
sound level
(dB(A))
27
27
30
31
31
27
24
27
25
28
25
27
26
27
27
25
26
26
24
26
26
24
31
67
67
65
58
59
54
57
54
55
55
55
55
55
69
69
69
69
69
69
69
69
69
54
94
94
95
89
90
81
81
81
81
83
80
82
81
96
96
94
95
95
93
95
95
93
85
214
278
321
321
350
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
113
113
113
113
113
113
113
113
113
226
70
90
90
90
110
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
90
90
90
90
90
90
90
90
90
82
104
125
146
145
155
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
100
100
100
100
100
100
100
100
100
127
780
1,450
2,400
2,450
2,750
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
490
490
490
520
520
520
520
520
520
1,500
68
69
70
70
70
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
65
65
65
65
65
65
65
65
65
n.d.
11
The most suitable lines of machines, then, are those of the modular type, including those most
widely present on the Italian market:
- TOTEM distributed by Tem;
- BIBLOC distributed by Savener.
It should be interesting, then, to analyze the characteristics of these two lines in detail.
TOTEM Line
The TOTEM line (produced in Italy) is supplied in three versions of the same power (if supplied
with the same fuel), preset to operate in parallel with other units of the same type (Figures 3 and
4):
Figure 3 - Basic diagram of the machines of the Totem line (standard version) (source: technical
documentation of the firm Tem).
1
electric motor
8 gas exhaust
2
water tank
9 electrical hookup
3
gas-water exchanger
10 hot water outlet
4
oil-water exchanger
11 cold water intake
5
oil tank
12 thermo-acoustic insulation
6
water-water exchanger
13 comburent intake
7
engine/electric generator
14 supply line
12
Figure 4 - Typical installation of a cogenerator of the TOTEM line
- Standard: operates using the electric mains for startup, generator excitation, and regulation. At
running speed and with natural gas, the machine delivers electrical power of 15 kW and
thermal power of 39 kW;
- Independent: designed for areas not served by the electric mains, this version also includes a 1.5
kW starter motor and a 12V 45 Ah battery. The electrical power supplied by the machine can
be regulated up to a maximum of 15 kW;
- Stand-by: combines the characteristics of the standard and independent versions; therefore, it
operates at constant power when connected to the mains, or at variable power in the "standalone" configuration (which can also occur following a power black-out).
All the models are characterized by a rotation speed of 3,000 rpm. A 1,500 rpm version has
recently been proposed, which is essentially the same machine (obviously the alternator changes)
with approximately halved power output. The TOTEM has a particularly high overall efficiency:
about 95% (25% electrical plus 70% thermal).
With reference to the 3,000 rpm machine, the main components are:
- thermic engine: which is the Fiat 100 GL type (0.9 litre displacement). In the latest models, the
FIRE type is also used (approx. 1 litre displacement). The system is particularly simple in the
standard type (the power supply is drawn directly from the mains), while in the independent
and stand-by types, the necessary energy is taken from the service battery.electric generator: the
3,000 rpm TOTEM machines are equipped with an asynchronous three-phase generator
(Ansaldo, with delta connection). In the standard version, the generator also serves as starter
13
motor. In the independent and stand-by versions, as the machines have to work in "stand-alone"
mode, they are installed in parallel to an excitation and regulation unit;
- primary hydraulic circuit: this is a closed circuit running with cooling liquid (2-3 m3/h of waterglycol mixture) that exchanges heat at different temperatures with four exchangers located, in
increasing order of temperature, on: the electric generator; crankcase sump; engine base;
exhausts. According to the machine design, the water enters, in order: the generator liner (in
cast iron), the oil exchanger (pressure cast aluminium), then continues to the thermal motor
liner (cast iron), and finally to the exhaust gas exchanger (pressure cast aluminium). The fumes
are cooled to 100°C. Subsequently, the fluid enters the plate-type exchanger (stainless steel)
connected to the secondary user circuit, where the related fluid is heated to a maximum
temperature of 86°C;
- gas and/or biogas feed system: in the standard version, it is formed by a main solenoid valve
and a pressure reducer; the mixing of gas with air takes place in a Venturi tube connected
downstream from the reducer. The pressure of the gas can range from 0.5 to 4 kPa;
- electronic regulation and control system: composed of a microprocessor, A/D converters
(analogue-digital), analogue signal transducers, and a display. The system controls the correct
operation of the machine in any type of use, stops it in case of operating problems, interlocks it
to external regulations, and signals the need for maintenance operations;
- frame: all the components are fitted on a chassis and insulated from the outside by panels and
doors that are thermally and acoustically insulated.
A comparison of the machines of the TOTEM line with the traditional type cogenerator
highlights the manufacturer's accomplishments in creating specific components, in particular heat
exchangers, and management software and hardware. The classic cogenerators, on the other
hand, are almost always the result of the experience accumulated in the construction of
generating sets and the precise assembly of standard components available on the market.
One qualifying aspect of the module in question which is sometimes underestimated is that it
resolves from the outset the problems of acoustic insulation and insulation from vibrations,
which are always costly to eliminate in the other cases.
As regards maintenance, operations are scheduled to be carried out every 1,250 operating hours
(reduced to 1,000 hours when using biogas supply). Maintenance on the exchangers is carried out
every 4-5,000 operating hours (every 6-7 months), and the engine and generator are normally
replaced with overhauled units every 10,000 operating hours. In any case, the most scrupulous
specialized firms check the motors at least once every two weeks and reduce the abovementioned invervals by 10-15% (about 4 years, including down times).
All things considered, the TOTEM line is perhaps currently the most reliable and tested small
size cogenerator. The key aspect is that of correct maintenance. Some units located in northern
Italy have worked more than 30,000 hours with biogas operation.
14
BIBLOC Line
The BIBLOC line (manufactured in Belgium) is composed of 5 models that differ in power and
type of thermic motor (the basic characteristics are shown in Tables 2 and 3).
All the models are characterized by a rotation speed of 1,500 rpm and operate in parallel with the
mains.
Like the TOTEM line, the BIBLOC line is composed of the following basic elements (see
Figures 5 and 6):
Figure 5 - Diagram of a machine of the BIBLOC line (90 kW electric). The other models are very
similar (source: technical documentation of the firm Savener)
A: plan view.
B: lateral view.
15
Figure 6 - Typical installation of a cogenerator of the BIBLOC line
- thermic engine: depending on the model, one of the following engines are used: Continental
TM27 (20 kW); Valmet 420G (30 kW) and 612G (60 and 90 kW); Scania DN11 (90 kW). All
the engines are otto cycle. The Continental is a four-cylinder engine (2.7 litre displacement)
specific for gas operation. The feed takes place through a diaphragm carburettor (that carries
out gas-fuel mixing) and is regulated, in the variable power versions, by a motor controlled by
the microprocessor of the cogenerator. The Valmet engines are diesel- derivated with four
cylinders (420G; 4.4 litre displacement) or six cylinders (612G; 7.4 litres). The 612G is a long
stroke engine particularly suitable for gas; the engine used for delivering 90 kW is also
supercharged. The feed is obtained with a carburettor plus ratio valve (Deltec) which, in
addition to pressure regulation, enables maintaining an air-fuel mix with fixed characteristics.
With biogas operation, it is recommended to create a feed line (gas ramp) in such a way that the
engine is run for about one minute before switch-off with a clean gas (LPG or mains natural
gas). This prevents the formation of acid condensates inside the cylinders and respective piping
during machine shutdowns;
- electric generator: all the models use four-pole asynchronous generators (Asae Brown Boveri)
without self-excitation device. The magnetizing current, then, is absorbed by the mains and this
16
requires power factor correction of the machine. The total efficiency (electric plus thermal)
varies from 86 to 91% depending on the load;
- primary hydraulic circuit: recovery takes place on the engine block (the fluid passes directly
into the respective cooling channels); oil (the exchanger is placed in parallel to the former, as
the fluid flow necessary for cooling is very low); exhaust gasses (using two monopipe
exchangers placed in series and operating in countercurrent). Subsequently, the fluid enters the
plate-type exchanger (stainless steel) connected to the secondary user circuit, where the related
fluid is heated to a maximum temperature of 85°C;
- gas and/or biogas feed system: in the standard version, it is formed by a main solenoid valve
and a pressure reducer; the mixing of gas with air takes place in a Venturi tube connected
downstream from the reducer. The pressure of the gas can vary from 0.5 to 4 kPa;
- regulation and control system: composed of a microprocessor control unit that monitors the
operating parameters and stops the machine in the event of malfunctions. A display makes it
possible for the user to check these parameters (temperature, pressure, rpm, etc.);
- frame: the assembly is contined in a metallic frame entirely covered with rigid panels in
soundproofing material.
It is clear, then, that the construction philosophy of the BIBLOC line is similar to that of the
TOTEM line. The BIBLOC, however, has considerably higher weight and bulk (remember that
the two lines are based on different rotation speeds).
1.4 Conclusions
Generally speaking, the majority of cogenerators present on the market have quite similar
structural and technical characteristics. In practice, they are derived from generating sets, with
the simple addition of heat exchangers and the necessary complementary controls. In this light,
the machines are basically constituted of components available on the market. This explains the
wide range of models available and their short commercial life.
The power levels are almost always greater than 100 kW.
The issue is different for the small units specially designed for disseminated cogeneration, which
are particularly interesting for farms in two aspects: power sizes congruent with the potential
biogas production; fewer installation problems (the machines are already complete, do not
require bases, and have simplified electrical and thermal connections).
In any case, it is of primary importance that a correct maintenance programme be carried out by
specialized companies.
As regards the economic aspect, each system should be evaluated according to the specific
project, and thus with design and setup costs that may differ for each installation. In general,
however, we can consider an overall investment that varies from 2,000,000 to 2,500,000 ITL/kW
17
electric installed (1,000-1,300 EURO/kW), considering only the electric and system hookup
operations.
2. SIZING AND INSTALLATION OF ENDOTHERMIC COGENERATORS
The aim of this section is to provide the basic elements and regulatory references for guiding the
choice, size, and installation of CHP plants powered by biogas used on pig farms.
The diagram in Figure 7 gives a quick picture of all the issues in this section: sizing, economic
verification and installation of biogas powered cogenerators. The diagram shows the flow of the
phases/activities related to the subject at hand. The references (composed of figures and/or tables,
included in progressive order) are highlighted in order to access the specific information.
PLANNING FASE
Energy analysis and
cogenerator sizing
(Figure 8)
Project
refuse
NO
Practicability verify
and acceptance
(Figure 9; Table 4)
YES
EXECUTIVE FASE
Laws, regulations, and
procedures
Contracts
Electrical plant
Hydraulic plant
Test
RUNNING FASE
Running
(Chapter 2.3)
Figure 7 - Flow-sheet: sizing, economic verification and installation and running of biogas
powered cogenerators.
18
2.1 Biogas production and sizing of the cogenerator
Figure 8 provides a diagram for estimating the production of biogas and sizing the cogeneration
system for pig farms with live weight present up to 1,000 t.
The live weight is shown on the horizontal axis of the abscissa of quadrant A, and the average
quantity of biogas that can be produced daily is shown on the vertical axis (m3/day). The two
straight lines represent the two most widely used systems: heated reactor, with conversion index
of 350 m3 biogas/t of live weight present * year; and unheated reactor with conversion index of
250 m3 biogas/t of live weight present * year. Quadrant B makes it possible to find the electrical
and thermal power of the cogenerator according to the number of operating hours per year
(considering: average electrical efficiency 25%; average thermal efficiency 60%; lower calorific
power of the biogas 23,000 kJ/m3, equal to approximately 5,500 kcal/Nm3). Quadrant C makes it
possible to calculate the quantity of electrical and thermal energy produced annually.
Example: on a farm with 500 t of live weight present and a heated reactor with average annual
conversion index of 350 m3/t l.w., the biogas production (quadrant A) is 480 m3/day. The
installable electric power (quadrant B), with the system operating 5,000 h/year, is equal to
approximately 55 kW, and the corresponding thermal power is equal to approximately 134 kW.
Quadrant C gives the energy produced annually: 275 MWh electric and 670 MWh thermal.
Similarly, a cogeneration system with electrical power of 24 kW that operates for 5,000 h/year
can be installed in a pig farm having about 300 t of live weight present which can produce about
205 m3 of biogas per day (average conversion index 250 m3 biogas/t of live weight present *
year). The related electrical energy production can be estimated at about 120 MWh/year, and the
thermal energy at about 287 MWh/year.
2.2 Economic analysis of the system
Figure 9 provides a diagram for calculating (with the help of Table 4) the number of years
necessary for recovering the investment made.
The axis of the abscissa of quadrant A gives the quantity of energy (electrical and thermal) that
can be produced with the cogenerator (result obtained from Figure 8). The axis of the ordinate
gives the annual gross benefit that can be obtained from the total transfer of the electrical energy
to ENEL (price: 270 ITL/kWh (0.14 EURO/kWh)). Quadrant B accounts for the cogenerator
operating costs. The axis of the abscissa gives the net annual benefit. In quadrant C the payback
time is calculated based on different initial overall investments: 100, 200, 300, 400 MITL
(million Italian lira) (50,000, 100,000, 200,000, 300,000 EURO).
19
Figure 8 - Provides a diagram for estimating the production of biogas and sizing the cogeneration system for pig farms with live weight
present up to 1,000 tons.
20
12
0,
5E
02
UR
5
O/
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EU
kW
03
RO
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75
EU
/k W
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RO
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G ra ss b ala n ce (E U R O .0 0 0)
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1 25
1 00
75
B
1
= 0,
EE
50
N e t b ala n ce (.0 0 0 E U R O )
1 75
1 50
1 25
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h
A
25
1 00
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1
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10
To t
al i
nv
es
te
m
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UR
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20
0
R
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O
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e
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2 00
3 00
4 00
5 00
6 00
7 00
E le ctric a l e ne rgy p rod u ctio n [M W h /y]
2
3
4
5
nt
(,0
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00
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7
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R
8
9
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P ay b ac k tim e (y)
C
r ic e
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rg y p
0 EU
e
n
=
E
E
T
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O /k
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35 E
Figure 9 - Provides a diagram for calculating (with the help of Table 4) the number of years necessary for recovering the investment made.
21
Table 4 - Indices for evaluating the point of economic indifference of an investment.
Time to
make
PNV=0
(years)
Interest rate (%)
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
1
0.94 0.93 0.93 0.92 0.91 0.90 0.89 0.88 0.88 0.87 0.86 0.85 0.85 0.84 0.83 0.83 0.82 0.81 0.81 0.80
1.5
1.39 1.38 1.36 1.35 1.33 1.32 1.30 1.29 1.27 1.26 1.25 1.23 1.22 1.21 1.20 1.18 1.17 1.16 1.15 1.14
2
1.83 1.81 1.78 1.76 1.74 1.71 1.69 1.67 1.65 1.63 1.61 1.59 1.57 1.55 1.53 1.51 1.49 1.47 1.46 1.44
2.5
2.26 2.22 2.19 2.15 2.12 2.09 2.06 2.03 2.00 1.97 1.94 1.91 1.88 1.86 1.83 1.81 1.78 1.76 1.73 1.71
3
2.67 2.62 2.58 2.53 2.49 2.44 2.40 2.36 2.32 2.28 2.25 2.21 2.17 2.14 2.11 2.07 2.04 2.01 1.98 1.95
3.5
3.07 3.01 2.95 2.89 2.84 2.78 2.73 2.68 2.63 2.58 2.53 2.49 2.44 2.40 2.36 2.32 2.28 2.24 2.20 2.17
4
3.47 3.39 3.31 3.24 3.17 3.10 3.04 2.97 2.91 2.85 2.80 2.74 2.69 2.64 2.59 2.54 2.49 2.45 2.40 2.36
4.5
3.84 3.75 3.66 3.57 3.49 3.41 3.33 3.25 3.18 3.11 3.05 2.98 2.92 2.86 2.80 2.74 2.69 2.64 2.58 2.53
5
4.21 4.10 3.99 3.89 3.79 3.70 3.60 3.52 3.43 3.35 3.27 3.20 3.13 3.06 2.99 2.93 2.86 2.80 2.75 2.69
5.5
4.57 4.44 4.31 4.19 4.08 3.97 3.87 3.76 3.67 3.58 3.49 3.40 3.32 3.24 3.17 3.09 3.02 2.96 2.89 2.83
6
4.92 4.77 4.62 4.49 4.36 4.23 4.11 4.00 3.89 3.78 3.68 3.59 3.50 3.41 3.33 3.24 3.17 3.09 3.02 2.95
6.5
5.25 5.08 4.92 4.77 4.62 4.48 4.34 4.22 4.10 3.98 3.87 3.76 3.66 3.56 3.47 3.38 3.30 3.22 3.14 3.06
7
5.58 5.39 5.21 5.03 4.87 4.71 4.56 4.42 4.29 4.16 4.04 3.92 3.81 3.71 3.60 3.51 3.42 3.33 3.24 3.16
7.5
5.90 5.69 5.48 5.29 5.11 4.93 4.77 4.62 4.47 4.33 4.20 4.07 3.95 3.84 3.73 3.62 3.52 3.43 3.34 3.25
8
6.21 5.97 5.75 5.53 5.33 5.15 4.97 4.80 4.64 4.49 4.34 4.21 4.08 3.95 3.84 3.73 3.62 3.52 3.42 3.33
22
To account for the interest on capital, Table 4 is used. If the maintenance costs and
investments are different from those indicated, the values are interpolated.
Example: In the case of total transfer to ENEL of 275 MWh/year, the gross annual benefit is
approximately 74.2 MITL (38,300 EURO) (quadrant A). The maintenance costs (quadrant B),
evaluated at 50 ITL/kWh (0.026 EURO/kWh), reduce the benefit by 14 MITL/year (7,200
EURO/year). Consequently, the net annual benefit is 60.2 MITL (31,100 EURO). The
resulting return on investment time in these conditions (quadrant C), for an initial investment
of 200 MITL (103,300 EURO), is about 3.3 years.
Table 4 completes the technical-economic evaluation initiated with Figures 8 and 9.
The payback time, calculated as the ratio between the initial investment and the net annual
benefits, provides a general indication of the profitability of the investment (this is the result
obtained with Figure 9). A more in-depth analysis must also account for the interest rate.
Normally, all the net annual benefits that can be obtained during the lifetime of the system are
adjusted to the year 0 (i.e. "transported" to the moment in which the investment is made). The
value obtained by subtracting the sum of all the adjusted net annual benefits is the PNV:
present net value.
The interest rate and the number of years of operation that make the PNV = 0 represent the
point of economic indifference (i.e. "installing" or "not intalling" the system is the same). It is
thus interesting to know after how many years the PNV becomes nil (that is, when the system
recovers the investment). Table 4 below is used for calcuating the PNV=0 time once we know
the payback time, obtained from Figure 8, and the interest rate. In the subsequent period of
operation, then, we obtain a "gain".
In the example described above, the point of economic indifference obtained with a payback
time of 3.3 years is 4 years considering an interest rate of 8%, or 5 years considering an
interest rate of 16%.
In this table, we can identify the values of the payback time closer to those obtained with
Figure 9.
2.3 General recommendations
This section offers general indications for the user who is interested in cogeneration and for
the system installers.
The heart of the cogenerator is the engine which, like all devices of this type, requires a
suitable maintenance programme. The engine, in fact, can reach and even surpass 5,000-6,000
h/year of operation. In this regard, it must be kept in mind that the most sophisticated
constructions, at 20-30,000 operating hours, require significant interventions on the basic
mechanics (special maintenance of the engine about every 4 years). The situation worsens
23
considerably if any anomalies occur during operation or in the presence of aggressive agents
(which biogas may be).
Consequently, the cogenerator should be viewed as an object to be monitored continuously
and to which adequate attention must be dedicated.
In general, the simplest and most economically feasible system design is that which involves
the installation of a cogenerator entirely dedicated to the mains.
In this case, the connection of the farm uses with the mains continues to be the traditional one,
governed by the type of contract considered most suitable. When the installed power is greater
than 20-30 kW, the "two-time slot contract for farm uses" is almost always the most
interesting, while for high power levels (greater than 100 kW), it is worth considering
contracts of the industrial type. The connection of the cogenerator, however, requires a special
line, on which it is not possible to branch a secondary line. This "dedicated" line, then, can
have only the devices for cogenerator protection and interface, together with the metering
instrument.
Another particularly important aspect concerns the quality of the biogas, which can vary in
composition and quantity depending on the meteorological conditions and farm management,
with the related consequences. The problem lies substantially in the biogas content of
moisture (it is, practically always saturated), inerts (in the form of dust or other), and sulphur
dioxide. Other problems derive from considerable variations in the CH4 content and the
pressure.
As a general rule, there are basically two possible solutions: to purify the gas as much as
possible or use the gas as is, making suitable modifications to the engine itself and using
special lubricating oils (with high TBN). The harmful effects of the sulphur dioxide are
drastically reduced if the conventional bearings in copper alloy are replaced with those in
white metal alloy.
In addition, it must be kept in mind that:
- dust and moisture are easy to eliminate (or at least to control) by using special wells for
condensate discharge, or better, cooling the gas appropriately;
- sulphur dioxide is difficult to eliminate in a constant manner over time, so it is advisable to
take the appropriate measures for the engine and the lubricant;
- continuous operation reduces the problems tied to the various contaminants of the gas.
Before switching off, it is advisable to use a "clean" fuel for a few seconds in order to
reduce the formation of aggressive deposits. This requires the creation of a special feed and
regulation line of methane gas or equivalent. The gas can be contained in cylinders.
Moreover, a special control unit must be installed when the switch-off procedure is to be
carried out automatically.
24
In the final analysis, all these factors influence the normal operation of the cogenerator and
must be keep in mind by the user and the installer when defining the respective business
relationships involved in the design and maintenance of the cogeneration system.
As regards maintenance, as a general rule it is certainly worth evaluating the contracts offered
by specialized firms that intervene regularly to carry out all the routine and special
maintenance operations. The contracts are always based on a fixed fee per kWh produced
(variable from 20-30 ITL (0.01-0.015 EURO) for the medium-large machines to 60-80 ITL
(0.03-0.04 EURO) for the small machines) up to 15-20,000 h of lifetime of the generator
(approximately 3-4 years, a period which is increased by using fuels other than biogas), after
which a flat rate is established for engine overhaul.
It is also helpful to keep a diary of operation which records the number of working hours and
any problems or anomalies found, in order to better evaluate the efficiency of the system.
3. REFERENCES
Associazione Elettrotecnica ed Elettronica Italiana (1986): Autoproduzione diffusa: problemi
e prospettive. Atti del Convegno tenutosi a Bologna il 21-22 maggio – AEI: 428 pp.
BIKLIM (1992): Documentazione tecnica sul Totem.
Cerizza F. (1980): Gruppi elettrogeni: installazione e conduzione. Editoriale Delfino, Milano:
107 pp.
Macchi E., Pellò P.M., Sacchi E. (1994): Cogenerazione e teleriscaldamento, aspetti
termodinamici ed economici. CLUP – Cooperativa Libraria del Politecnico di Milano: 240
pp.
SAVENER (1993): Documentazione tecnica relativa ai cogeneratori.
Thermie programme (1992): A review of cogeneration equipment and selected installation in
Europe. Maxibrochure disponibile presso i Centri OPET della Commissione della EU: 19 pp.
Thermie programme (1992): Small-scale cogeneration in non-residential buildings.
Maxibrochure disponibile presso i Centri OPET della Commissione della EU: 20 pp.
25