GHG/07/48
IEA GREENHOUSE GAS R&D PROGRAMME
32nd EXECUTIVE COMMITTEE MEETING
USE OF BIOMASS WITH CCS
(Proposal number 32-1)
Introduction
Combustion plants which use sustainably grown biomass can be deemed to have near zero net CO2 emissions, because the CO2 emitted to the atmosphere is assumed to be absorbed by growth of the biomass fuel. If the CO2 is captured and stored, instead of being emitted to the atmosphere, the net emissions would be negative. The ability to generate energy while reducing the quantity of CO2 in the atmosphere would be a unique feature of biomass fired plants with CCS.
Another option would be to co-use small proportions of biomass in coal-fired plants with CCS, to achieve zero net-CO2 emissions.
In 1997 IEA GHG carried out a study to assess the costs of small scale (20-60 MWe) biomass fired power plants in Spain but that study did not consider CO2 capture.
Biomass sources and utilisation technologies
Most of the biomass that is currently used for energy production is by-products and residues, including bark, sawdust, straw, palm kernels, rice husks, sugar cane bagasse and black liquor from pulp mills. Much of these materials are already used for energy production. Biomass can also be produced specifically as a source of energy, for example crops for production of liquid fuels (bio-diesel and ethanol), and fast-growing wood, grasses etc. for heat and power production.
In some regions, e.g. the EU and USA there are incentives to increase the use of biomass to reduce greenhouse gas emissions and reduce the dependence on imported fossil fuels. This means that use of biomass energy crops is likely to increase in future, although there are some concerns regarding the impacts of this on food availability and prices and increased deforestation.
Biomass can be used in the following types of plants:
§ Combustion of biomass on its own in heat and/or power generation plants
§ Co-combustion of biomass and coal, usually in larger power plants
§ Gasification of biomass on its own in heat and/or power generation plants
§ Co-gasification of biomass and coal, usually in larger power plants
§ Fermentation and other types of plants for liquid fuels production.
Plants which use solely biomass are usually smaller than coal-based plants, because the quantities of biomass that can be grown close to a plant are limited and biomass has a relatively low density and high transport costs.
The CO2 capture processes that could be used in biomass combustion and gasification plants are similar to those that would be used in coal fired plants of similar sizes. Applicable capture technologies include post-combustion, pre-combustion and oxy-combustion capture.
There are therefore many combinations of types of biomass, types and sizes of utilisation plant and types of CO2 capture process. Detailed assessment of the many possible combinations would be unrealistic. This study will therefore include a high level comparison of biomass and coal based plants with CO2 capture and a more detailed assessment of selected cases.
Outline scope of the study
The aim of this study is to assess the costs of CO2 capture in biomass utilisation plants. The broader issues of the advantages and disadvantages of biomass as an energy source and sustainability issues are beyond the scope of the study. The study will include the following major tasks:
Biomass types
The main types of biomass and their analyses will be summarised. This will include by-products, residues and purpose-grown biomass.
Combustion and gasification plants
The main factors which would be different between CO2 capture units in biomass and coal combustion and gasification plants will be identified. These could include for example flue gas CO2 concentration, quantity of CO2 per unit of useful energy, impurities concentrations and typical plant sizes. Significant differences between different types of biomass will be identified.
The implications of these differences for CO2 capture processes will be discussed. Any factors which may make certain capture technologies more or less suitable for biomass-based plants would be identified.
CO2 capture in liquid fuels production plants
Processes for producing bio-ethanol and bio-diesel will be described. Opportunities for co-production of heat and power in these processes will be identified.
The CO2 capture processes which could be used in bio-ethanol and bio-diesel plants will be identified and compared.
Life cycle emissions
The life cycle emissions of greenhouse gases associated with production and delivery of various types of biomass will be complied from published information and contacts with other organisations
Taking into account life cycle emissions associated with fuel production and delivery, the quantities of biomass that would have to be used in a co-combustion plant to achieve zero net CO2 emissions will be estimated. The feasibility of co-combusting the required quantity of biomass will be considered.
Assessment of selected cases
Four cases will be selected for more detailed assessment of CO2 capture plant performance and costs. The cases will be selected during the course of the study but they may include for example a large ‘zero net CO2 emissions’ co-combustion power plant, a large plant using only purpose grown biomass (e.g. in the US mid-west or Brazil), a smaller combined heat and power plant using biomass by-products or residues and a liquid fuels production plant.
The energy consumptions and costs of CO2 capture in these plants will be estimated.
The sensitivities of costs of capture to various technical and economic parameters, including plant size, biomass price and economic discount rate will be presented graphically.
Collaboration with other organisations
The IEA Bio-Energy Agreement and other relevant organisations will be contacted to ensure that existing information and expertise on biomass analyses, utilisation technologies and life cycle emissions is used as far as possible.
Proposal
It is proposed that a study should be carried out on the use of biomass with CCS.
RESOURCES REQUIREDFinancial / Project management
Average / Average
The committee is requested to
i) Approve proceeding with this study.
ii) Suggest possible contractors
iii) Suggest possible expert reviewers for the completed study
2