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Integration of biogas systems into the energy system
Technical aspects of flexible plant operation
Jan Liebetrau Rytec
Peter Kornatz DBFZ
IEA Webinar 21 January 2021
www.ieabioenergy.com2
Authors:
Jan Liebetrau (Rytec, Germany),
Peter Kornatz (DBFZ, Germany),
Urs Baier (ZHAW, Switzerland)
David Wall & Jerry D Murphy (MaREI centre, University College Cork, Ireland)
https://task37.ieabioenergy.com/files/daten-
redaktion/download/Technical%20Brochures/Flex%20rep
ort_END_WEB.pdf
Find the report on the Task 37 web site under:
A Technical report from IEA Bioenergy Task 37
www.ieabioenergy.com3
• Introduction - Flexibility in the context of biogas systems
• Technical aspects of flexible plant operation
• Economics
• Exemplars of flexible operation
• Conclusion
Outline
Reasons for demand oriented operation
4
• Biogas based electricity as an facilitator for increasing share of
fluctuating renewables on different grid levels
• Direct supply of fluctuating demand of industrial facilities or
energy customers, also in areas with instable grid situation,
biogas as stand alone solution
• Reaction on maintenance shut down on site
• Biogas as a potential link between electricity and gas grid
(Power to gas - storage and distribution option)
Agora Energiewende: 12 insights on Germany's Energiewende February 2013
5
Electricity demand of a dairy farm in Summer (Neiber, 2020)
Demand electricity - different levels
• Depending on the energy customer required flexibility can have complete different requirements
• Grid connection or stand alone?
• Is on site storage (gas, electricity, heat) available?
6
Demand on the heat site
Development of main heat utilization in Germany for 2010-2017 (Daniel-Gromke et al., 2019a)Typical heat demand for heating and hot water supply of buildings with mixed
residential and industrial use (Jan Liebetrau, Rytec, own data 2020)
• Heat follows seasonal fluctuations, depending on the type of heat use
• Heat dominated CHP operation is done in Germany occassionally
7
Demand on fuel supply – fleet supply
Aggregated fuel demand function for a truck fleet and an agricultural business. (Gögköz et al., 2020)
• Only with fleets somewhat predictable
• Stand alone fuel station has to be developed.
Only relevant in case of stand alone fuel station
Technical options for flexibility on site
8
• Flexibility results in reduced capacity utilization or overcapacity is necessary
• This results in higher technical effort and costs, which have to be balanced by
the benefits
• Increase of CHP capacity (and grid access)
- in case of constant annual energy output
• Increase of gas storage capacity
• Control of biogas production rate
(controlled feeding,
storage of intermediates)
• Power to heat
• Biomethane
• Power to gas
Quality of flexibility – control aspects
9
Limited flexibility with standardized fluctuation(e.g. electricity market price oriented)
Flexibility on demand (e.g. ancillary services)
Prognosis step
IEA Bioenergy Conference 2015, Berlin October 2015
Time (h)
Time (h)
Ele
ctri
cal
cap
acit
yEl
ect
rica
lca
pac
ity
10
Schedules and markets
Weekly schedule Daily schedule Real time control
Brief description Weekly fixed scheduleNext day individually optimised
schedule Optimised during the day
Serviceable marketsDay ahead
Ancillary services
Day ahead
Ancillary services
Day ahead,
Intraday,
Ancillary services
Technical effort,
remote control
low,
optional remote control(ancillary services require remote
control)
Medium,
Indirect or direct remote control(ancillary services require remote control)
High,
Direct remote control (ancillary services require remote
control)
RestrictionsBiogas production (substrate availability), number of starts and stops of CHP, gas storage
capacity, heat demand, limits of capacity utilization, min/max performance
Flexibility/revenue low medium high
Main characteristics of basic schedules for flexible operation (Daniel-Gromke et al., 2019b)
11
• Preheating of cooling water and oil (min. 60 °C);
• Optimized starter and starting procedure of the CHP;
• Recirculation of air in air conditioning;
• Electric oil pressure build up prior to the starting procedure;
• Constructive condensation traps;
• Stainless steel finish at weak points due to sulphuric acid in condensate;
• Remote monitoring and control options for the CHP – PLC;
• Changing requirements for biogas quality (sulphur content, temperature, moisture).
CHP operation on flexible plants
12
CHP operation on flexible plants
Part load operation and efficiency of selected biogas CHPs (Tappen et al. 2017)
100 %
Load
(203 kW)
90 %
Load
(183 kW)
80 %
Load
(162 kW)
70 %
Load
(142 kW)
60 % Load
(122 kW)
Efficiency 33.7 % 31.6 % 31.3 % 29.5 % 27.4 %
CH4
slippage
0.47 % 0.52 % 0.58 % 0.65 % 0.74 %
Part load and methane slippage (Lichti et al., 2018)
Increasing capacity has higher electric efficiency - one large engine is more
efficient than two smaller engines combined
13
Flexible operation – gas management
• Gas storage balances deviation between gas production rate and gas
utilization rate
• Gas storage capacity is limited
• Gas management often not made for flexible operation
(e.g. effectively available gas storage capacity)
14
Potential measures to improve (Reinelt et al. 2019):
• Installation of additional (clean) gas storage;
• Upgrade of sensors for precise filling level evaluation;
• Installation of a gas management (transportation) system between the gas domes via
a controllable blower for inflation air;
• Upgrade of gas transportation lines;
• Upgrade of gas treatment devices.
Flexible operation – gas management
15
Flexible operation – gas management
• Gas storage balances deviation between gas production rate and gas
utilization rate
• Gas storage capacity is limited
• Feeding management can alter gas production rate to provide gas
when needed
• Model based control gives information on gas production rate of
substrate mixes
16
set variable:
substrate type
feeding amount
control variable:
gas storage filling level
Mauky et al: Chem. Eng. Technol. 2016, 39, No. 4, 652–664 DOI: 10.1002/ceat.201500412
Block diagram of the applied model predictive control (MPC) algorithm
Control of biogas production rate
Controlled biogas production
Gas
pro
du
ctio
n/g
as u
tiliz
atio
n(m
³/h
)G
as s
tora
gefi
llin
gle
vel(
m³)
Time (d)
Forward-looking process
management according to a
given schedule of energy demand
Component design needs to be
adjusted to variable energy
provision, flexibilisation can have
an impact on all components of
processing
Mauky et. Al, 2016: Model predictive control for demand driven biogas production in full scale, Chem. Eng, Technol. 2016, 39, No 4
45% Less gas storage
capacity
18
Process optimization including external factors
Source: DBFZ 2019
Flexibilisation
requires the
integration of
external factors and
internal limitations
Increasingly
complex
optimisation tasks
and complex
monitoring and
control tasks
Example for a more comprehensive process control considering technical and economic requirement (data from DBFZ) (EPEX: European power exchange – market for electricity)
Influence of solar radiation on gas storage capacity
SEITE 19
a) total view with normal
camera modus and
b, c, d): measured by
Infrared camera; cross
indicates the location of
the respective maximal
value
Source: Mauky/DBFZ
20
Influence of solar radiation on gas storage capacity
Based on Mauky et al. (2017)Demand-driven biogas production in full-scale by model predictive feed control.Conference Proceedings of the 25th European Biomass Conference and Exhibition (EUBCE), Stockholm, Sweden , S. 1845-1851
Up to 20 % difference in capacity
Intraday temperature difference [°𝐶]:5.1 → 29.7 = 24.6 March8.4 → 33.5 = 25.1 April8,7 → 37,7 = 29,0 April
11.0 → 34.2 = 23.2 May16.8 → 42.5 = 25.7 July 13,2 → 40,8 = 27,6 August23.6 → 43,4 = 19.8 September
7 %
13 %
20 %
21
Economics of flexible operationGeneral economics – aspects have to be considererd
Aspects have to be considered about
economy:
• Capex and opex for a given degree of
flexible operation
• Additional installation
• Additional maintenance effort
• Costs related to decreasing capacity
utilization
• Revenues and contracting conditions for the
energy products
• Long term prognosis of the energy marketsSource: Barchmann, DBFZ
22
Economics of flexible operationGeneral economics – difference between base load plants and flexible plants
concerning production cost
• Cost-based approach with new
constructed biogas plants
• no national specific assumptions
regarding funding systems
• 500 kW agriculture biogas plant
as example
• Feedstock: 30 % manure, 40 %
maize, 30 % sorghum
• One more CHP-unit at the
same annual power
production level, means
approx. 3 €ct/kWh higher
production cost
Reference
none 2 2 4
Base load operation Flexibilisation Downsizing Flexibilisation Upsizing Flexibilisation Upsizing
Installed power 500 500 1.000 2.000
Nummer CHP units 1 1 2 4
Operation time h/a 8.000 4.000 4.000 2000
Power sold kWh/a 3.960.000 1.980.000 3.960.000 3.960.000
Component Investment Investment Investment Investment
[€] [€] [€] [€]
CHP 453.902 453.902 907.804 1.815.608
Flare 123.288 77.163 123.288 123.288
Pumpstation 64.844 41.173 64.844 64.844
Solid feeding unit 336.956 186.622 336.956 336.956
Digester 505.077 297.236 505.077 505.077
Digestate Storage 379.326 228.615 379.326 379.326
Gasstorage 95.320 95.320 170.213 680.853
Sum of investment 1.958.713 1.380.031 2.487.508 3.905.952
Planing and constrution preparation 195.871 195.871 195.871 195.871
Complete investment for biogas plant 2.154.585 1.575.902 2.683.379 4.101.823
Annual cost (20 years operating time)
Capex [€/a] 294.618 223.029 394.032 687.831
Opex feedstock and resources [€/a] 403.479 201.740 403.479 403.479
Opex misc [€/a] 42.395 42.395 42.395 42.395
Sum [€/a] 740.492 467.163 839.906 1.133.705Specific cost
Power production cost [€/kWh] 0,187 0,236 0,212 0,286
Difference to reference[€/kWh] x 0,049 0,025 0,099
Flexibilisation factor
Flexibilisation options
23
Taking part in the electricity market leads
to a so called „double hump“, which define
the times of high prices and the preferred
times of electricity feed in
Demand translates into price development
Example of daily price development of day ahead market in 2020 (Auction
Day Ahead, 60 min, Germany, 31 of January 2020, Baseload (Source: EPEX
SPOT))
24Example of daily price development of day ahead market in 2020 (Auction Day Ahead, 60 min, Germany, 31 of January 2020,
Baseload (Source: EPEX SPOT))
Economics of flexible operationGeneral economics – revenues of flexibilisation (market)
economic efficiencythreshold for double flexible
option
Activation time CHP (6h)
Activation time CHP (6h)
• higher expenses must be compensated
by interacting with the volatility of the
market
• Market potential is very limited for the
payment of flexibility
• Expected additional revenues approx. 0.5
till 1.5 €cent/kWh in average
• Maximum values can be much higher
• Possibility for additional revenues
depends on price spread
25
Economics of flexible operationGeneral economics – revenues of flexibilisation (market)
Source: Dotzauer, 2020
• higher expenses must be
compensated by interacting with
the volatility of the market
• Market potential is very limited for
the payment of flexibility –
additional revenues needed!
(Heat, Summer Winter etc .)
• Expected additional revenues
approx. 0.5 till 1.5 €cent/kWh in
average
• How will the future look like?
Conditions for market products
26
Source:Barchmann et. al. 2016
• Different market options with different requirements for participation
• Biogas plants have individual constructive and operational designs –
which define the limits of flexibility
9/2018:
2.927 Plants (biogas+biomethane)
eligible for extra tariff „Flexprämie“
(app. 2,02 Gwel)
0
250
500
750
1.000
1.250
1.500
1.750
0
500
1.000
1.500
2.000
2.500
3.000
Insta
llie
rte
ele
ktr
isc
he
An
lag
en
leis
tun
g [M
We
l]
An
zah
l B
HK
W [n
]
Anzahl Biogas-BHKW, [n] Anzahl Biomethan-BHKW, [n]
install. el. Leistung Biomethan-BHKW, [MWel] install. el. Leistung Biogas-BHKW, [MWel]
Σ Biogas-BHKW n = 2.678
Σ Biomethan-BHKW n = 342
© DBFZ 08/2018
Incentives for technically „standby“;
this does not mean process
flexibilisation in operation
Number of biogas CHPNumber of biomethane CHP
Install. el. capacity biogas CHP (Mwel)Install. el. capacity biomethane
CHP (Mwel)
Exemplars of flexible operationDevelopment of flexibilisation in Germany (CHP and biomethan-CHP)
Source: DBFZ, based on annual power generation in respect to BNetzA 2012 – 2016, plant register of BNetzA 08/2018 and monthly reports of power trading companies 2012 - 2018
Number of biogas CHP
28
Bioenergie Langwedel GmbH & Co. KG
Basic information:
•Commissioned in 2010;
•Substrates include for over 50% liquid cattle slurry and dung, less than 30% corn silage with the
remander of feedstock comprised of cereal crop silage and cereals;
•Flexibile operation in place since February 2019;
•The average output is 486 kW;
•Installed capacity of 2,356 kW via three CHP units;
•The maximum gas storage capacity (at average gas production) is 16 hours;
•The volume of storage is 5.000 m³
•Heat storage of 1,000 m3 of hot water
Marketing concept:
•Individual electricity market oriented operation for the following day (day ahead market) and participation in “intraday” market;
•Both CHP units have approximately 1,800 h/a full load operation;
•Remote control from electricity trader;
•The contractor can directly access the process and process relevant parameter;
•Additional income expected in 2019 of more than 1.5 ct€/kWh;
•Operate with a maximum of 2 starts per day with a minimum of 1 hour of operation with both CHP units in full load, shift of electricity production to winter;
•The heat from the CHP unit is used to heat buildings and barns and dry digestate;
•95 % of available heat is used.
Exemplars of flexible operationExamples for flexible biogas plants
29
Bioenergie Hotteln GmbH & Co. KG
Basic information:
•Commissioned in 2018;
•Substrates include maize and suger beet
•Flexibile operation in place since February 2019;
•The average output is 486 kW;
•Installed capacity of 2,356 kW via three CHP units;
•The maximum gas storage capacity (at average gas production) is 14 hours;
•The volume of storage is 5,000 m³;
•Heat storage of 250 m3 of hot water
Marketing concept:
•Individual electricity market oriented operation for the following day (day ahead market) and participation in “intraday” market;
•Both CHP units have approximately 1,800 h/a full load operation;
•Remote control from electricity trader;
•The contractor can directly access the process and process relevant parameter;
•Additional income expected in 2019 of 0.5 ct€/kWh;
•Operate with a maximum of 2 starts per day
•The heat from the CHP unit is used to heat residential buildings an two hotels, furthermore a drying unit is included
•100 % of available heat is used.
Exemplars of flexible operationExamples for flexible biogas plants
30
The Swiss virtual power plant “Fleco Power” represents a marketplace to match flexibility of
producers and users of new renewable energy.
The flexibility of over 80 biomass, small hydroelectric and photovoltaic plants with a nominal power
of 30 MW is bundled and marketed as control energy to Swissgrid, the Swiss electricity grid
operator.
Fleco Power Structure to combine flexibility of decentralized installations
Exemplars of flexible operationFlexibilisation in Switzerland – Virtual Power Plant
Source: IEA Bioenergy 2020
31
Example of a 1-day flexibility control time course of a biogas installation in Switzerland in Autumn.
green: peak load time windows. blue/red: Historical load curves of electricity demand.
violet: biogas CHP timetable
Exemplars of flexible operationFlexibilisation in Switzerland – Virtual Power Plant
Source: IEA Bioenergy 2020
www.ieabioenergy.com32
The perception of the role of biogas has changed from traditionally seen as a means of treatment of a range of wet organic wastes towards a source of renewable energy as part of a new energy system.
In the near future the integration of energy vectors will be essential in facilitating PV during daylight hours, wind power on windy days and renewable sources of dispatchable energy such as from bioenergy.
The biogas plant operation itself can be controlled extensively and with this control comes high levels of flexibility.
Biogas systems can be a node of integration between electrical and natural gas grids in providing a sink for electricity (through power to gas systems) that would otherwise be curtailed or constrained.
The flexibility of biogas systems can facilitate energy delivery to:
• the electricity grid as close as possible to the electricity demand profile
• heat to consumers facilitating the seasonal demand profile of heat;
• to the gas grid to decarbonize gaseous fuels for various purposes;
• Biomethane directly to local consumers such as for transport biofuel for haulage and buses;
• Biogas can play an essential role as part of a virtual power plants.
Conclusion
www.ieabioenergy.com
Thank you for your interest
Contacts:
Jan Liebetrau
Rytec GmbH
Peter Kornatz
DBFZ
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