generation of electricity and heat from biomass...biomass herbaceous / crop residue seeds, husks and...
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Generation of electricity and heat from biomass:
Technology options and potential pitfalls
Nick Ash
Principal Consultant
Ricardo Energy & Environment, U.K.
RICARDO ENERGY & ENVIRONMENT…
…provides strategic consultancy and project leadership for national and local governments, the European Commission, multinational
corporations and a wide range of public and private sector organisations in these sectors:
Owned by Ricardo plc
RICARDO ENERGY & ENVIRONMENT…
…has a portfolio of more than 200 projects delivered in Africa in the Energy sector…
Countries shaded blue indicate Ricardo Energy & Environment project references
…and a Johannesburg-based subsidiary, PPA Energy (Pty) Ltd.
WHAT WE’LL COVER IN THIS SESSION
Benefits & drawbacks of
biomass
Specialist advice for
project development
Fuel considerations
Technology options
Conclusions
BENEFITS & DRAWBACKS OF BIOMASS
THE BENEFITS OF BIOMASS
A renewable energy source to substitute
fossil fuels
A dispatchable technology to complement
fluctuations in solar, wind & hydro
Provides a sustainable approach to managing
bio-waste from agriculture & industry
Can allow processing plants to reduce reliance
on electricity from the grid
Potential additional revenue stream(s) for
processing plants through sale of
electricity and/or heat
Processing plants often require heat, creating an opportunity for higher-efficiency cogeneration
Can provide enhanced energy security as an
additional (home-grown) energy resource
Potential for development at a range
of scales drawing on local resources
Can be a catalyst for local economic
development, up-skilling and increased employment
BUT THERE ARE SOME DRAWBACKS
In a shifting environment where the capital costs of solar, wind and storage facilities are decreasing…
• Investment decisions need to be made carefully considering the full lifecycle costs & benefits
Leve
lise
d c
ost
of
ele
ctri
city
($
/MW
h)
Source: Lazard (2017)USA
Source: BEIS (2016)UK
Source: Ricardo (2016)South Africa REIP Round 3
50
80
110
Biomass combustion plants already have a higher LCOE
than onshore wind and utility-scale solar PV
Onshore wind
Utility-scaleSolar PV
Biomass boiler plant
CONSIDER THE BUSINESS CASE CAREFULLY
Without government support, it can be difficult to make a business case for a biomass plant that only exports electricity
• Existing processing plants with biomass by-products are ideal candidates
• Where self-generation can reduce reliance on imported electricity
• The business case is enhanced further where there is also a demand for heat (increased efficiency through cogeneration)
It should be considered as one technology option in a coherent energy strategy
• Through integrated resource planning
The economic benefits to the local community should be considered in addition to the financial aspects…
• But this is difficult for a developer to justify financially (internalize)
SPECIALIST ADVICE FOR PROJECT DEVELOPMENT
SPECIALIST ADVICE IS REQUIRED TO…
Assist with project technical, financial and legal preparations
Prepare and evaluate the business case
Manage project-specific risks
Prepare project documents
This is especially the case if you need to secure external financing
CONSIDERATION MUST BE GIVEN TO THE FULL PLANT LIFECYCLE
• Fuel availability & properties
• Grid connection
• Site availability
• Plant technology
Feasibility stage
• Capital costs
• Financing
• Risk management
Financing, design, procurement, construction • Sale/substitution of
electricity & heat
• O&M costs
• Reliability
Operation
• Environmental impact
• Social impact
Decommissioning
Enabling environment is critical
Government policy supportLegal frameworkRegulatory environmentPlanning & ESIA processesMarkets for electricity and/or heat
THIS SESSION WILL CONCENTRATE ON FUEL CONSIDERATIONS AND TECHNOLOGY OPTIONS
And the implications
for O&M
Can you get the feedstock at the required:• Cost• Quantity• Quality • TimeTo produce the energy required?
Will you be able to sell/use the energy you produce?
FUEL CONSIDERATIONS
ASK YOURSELF: WHERE WILL I GET THE FUEL AND IS THERE ENOUGH?
• The amount of fuel available will determine the plant output in terms of electricity/ heat
Availability and cost of feedstock
• Haulage costs in Africa are significant
• Long distances increase risk of supply disruptions
Site location is critical
• Cost of fuel, transport and preparation required
• It has a direct influence on the business case
Cost of feedstock
• Mitigate against supply uncertainty
• Long term agreements mitigate against short-term fuel price volatility
Fuel supply agreements
ASK YOURSELF: WILL THERE BE A RELIABLE FUEL SUPPLY?
• Availability of suitable vehicles in sufficient quantities
• Quality of roads
Transport infrastructure
• Logistics of delivery vehicles to provide a steady fuel supply
• Avoidance of bottlenecks to minimise weighing and offloading time
Fuel offloading efficiency
• Supplementary sources in the off-season of the primary fuel
Seasonal variations
• As a buffer to compensate for supply disruptions
Storage facilities
THE CHEMICAL PROPERTIES OF THE FUEL DETERMINE THE PLANT TECHNOLOGY
Calorific value
Moisture content
VolatilesAsh
content
DON’T IGNORE THE ASH CONSTITUENTS
Biomass fuels tend to have high proportions of alkali-earth minerals in the ash
Alkali oxides are associated with boiler “fouling“ (insulation), reducing efficiency
Fouling can be minimised by increasing furnace height
Fouling indices can be used to predict fouling propensity
High silica content tends to mitigate against fouling
OTHER NASTIES TO BEWARE OF
Higher combustion temperatures increase
the risk of aggregation of solid materials in the
boiler, called “slagging”
This is also dependent on ash properties
Check for high concentrations of
sulphur and chlorine in the fuel
These can form acids within boilers and lead to
accelerated corrosion
PLANT TECHNOLOGY OPTIONS
BIOMASS PLANT TECHNOLOGY OPTIONS FOR AFRICA
Grate boiler
+ steam turbine
Fluidised bed boiler
+ steam turbine
Thermal gasification + engine /
gas turbine
Anaerobic digestion + engine /
gas turbine
GRATE BOILER + STEAM TURBINE
Mature technology; unit sizes up to ~40 MW
Relatively reliable; moderate operator skill required
Used throughout Africa for many decades
Relatively limited fuel range; suited to solid fuels with moderate moisture (40 – 55%) content
Prone to fouling with high-alkali fuels (high combustion temperature)
Efficiency of converting fuel to electricity ~30% (assuming no cogeneration)
Lowest capital and operational costs of options presented here (similar to fluidised bed boiler)
Large ash residue volume requires disposal/storage; risk of NOx, SOx & particulate emissions (depending on fuel)
Source: John Thompson Boilers
Note: It is possible to clean up gaseous emissions, but this adds cost & complexity
FLUIDISED BED BOILER + STEAM TURBINE
Source: ESB
Mature technology; unit sizes can be greater than 40MW
Relatively reliable, but require highly skilled operators
Limited references in Africa, especially for biomass applications
Suitable for wide range of fuels (but not wide variations in one application)
Some fouling with high-alkali fuels (lower combustion temperature than a grate boiler)
Efficiency of converting fuel to electricity ~30% (slightly higher than equivalent grate boiler)
Lowest capital and operational costs of options presented here (similar to grate boiler)
Large ash residue volume requires disposal/storage; risk of NOx, SOx & particulate emissions (depending on fuel)
Note: It is possible to clean up gaseous emissions, but this adds cost & complexity
THERMAL GASIFICATION + ENGINE / GAS TURBINE
Source: Siemens
Emerging technology for biomass; unit sizes up to ~10 MW
Complex plant (esp. for syngas cleaning) requiring highly skilled operators
No known references in Africa at industrial scale
Limited variability in feedstock tolerated (high moisture fuels require drying)
Good for high-alkali fuels due to absence of combustion
Efficiency of converting fuel to electricity ~20%
Highest capital and operational costs of options presented here
Large ash residue volume requires disposal/storage; complex clean-up to remove NOx, SOx & particulates
Note: Syngas can also be processed to produce chemicals or liquid fuel.
ANAEROBIC DIGESTION + ENGINE / GAS TURBINEMature technology; unit sizes up to ~4 MW (small-scale
applications)
Relatively reliable but biogas clean-up equipment adds complexity; requires moderate operator skill
Multiple project references in Africa
Sensitive to feedstock variability; best suited to high moisture & starchy fuels*
Good for high-alkali fuels due to absence of combustion
Efficiency of converting fuel to electricity ~40%
High capital and operational costs (lie between boiler plant & gasification)
Digestate by-product is a good fertiliser; lower risk of harmful gaseous emissions than boilers or gasification
* Anaerobic micro-organisms can’t break down the lignin within wood products and straw.
Additional note: Large land area per unit electricity produced compared with other options quoted here.
PLANT TECHNOLOGY OPTIONS AND FUELS
Technology Woody biomass
Herbaceous/ crop residue
Seeds, husks and shells
Food and animal wastes
Liquid residue/ wastes
Grate boiler + steam turbine
Fluidised bed boiler + steam turbine
Thermal gasification + engine / gas turbine
Anaerobic digestion + engine / gas turbine
CONCLUSIONSBiomass has many benefits, but it should be considered as one
option in an integrated resource plan
Develop a comprehensive understanding of the fuels from the start of the project
Ensure that there will be buyer(s) of the energy products for the full life of the plant
To navigate the many risks, engage specialist advisors from the feasibility stage to commercial operation
Select the technology to suit the fuels and skill base of O&M personnel
Ensure the technology has an established, comprehensive support network within Africa
BIBLIOGRAPHY
• BEIS (2016) Electricity Generation Costs.
Department for Business, Energy & Industrial
Strategy, Govt. of United Kingdom, London.
• International Finance Corporation (2017)
Converting Biomass to Energy. International
Finance Corporation, Washington D.C.
• Lazard (2017) Lazard’s Levelised Cost of
Energy Analysis – Version 11.0.
• Magasiner, N. et al (2001) Characterising Fuels
for Biomass-Coal Fired Cogeneration. Proc. S.
Afr. Sug. Technol. Ass., Durban.
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