COMPARING COMBUSTION TO GASIFICATION
Regardless of vendor claims and the hype surrounding other thermal conversion technologies such as gasification, combustion remains the most reliable and cost effective thermal conversion technology offering unparallel fuel flexibility, low maintenance requirements, high availability and ultimately superior financial results.
01. TECHNOLOGY MATURITY
Biomass combustion is a mature, extensively field tested and commercially available technology that currently accounts for over 90% of the biomass used for energy purposes. Biomass gasification on the contrary is far from being considered a technology sufficiently mature for commercial deployment.
Quoting from the European Biomass Industry Association: “After a long lasting development, which dates back to the 18th century, the commercial implementation of biomass gasification is still problematic. Very few processes have yet proved economically viable,”. (link)
Graph Source: EPRI
02. REFERENCES
Although records on operating biomass gasification plants are scarce, several facilities have ceased operations due to technical and financial problems.
According the Gasification Technologies Council database, (link) as of today, less than 15 power plants based on biomass/waste gasification operating worldwide. As an order of magnitude, Turboden biomass plants alone count more than 220 plants.
Furthermore, in addition to existing plants, and according to Bloomberg’s New Energy Finance 94% of all proposed biomass power generation projects (10 GW) that are either under construction or have secured financing for 2013 are based on combustion.
Graph source: Bloomberg New Energy Finance
03. RELIABILITY
Biomass gasification power plants have long been plagued by technical and financial problems which often led to cease of operations.
Syngas cleanup and the efficient removal of tar are yet to be addressed; the simple scrubbing approach has failed repeatedly to prove long term operational reliability and in addition it creates a serious environmental problem because of the large quantities of condensate produced.
Effectively, failure in removing tars remains the main technical barrier for the use of syngas in internal combustion engines; in many cases engine damage has been the main cause for shutting down biomass gasification power plants.
Furthermore, syngas is highly combustible and often contains high levels of carbon monoxide. As syngas cannot be stored operation at partial load is problematic. These characteristics along with the overall operational complexity of gasification systems often require specially trained personnel.
04. EFFICIENCY
Owing much the technical problems with syngas cleanup, the use of internal combustion engines in biomass gasification plants has proved problematic. Operational experience with gasification suggests that reaching the claimed electrical efficiency figures based on the combustion of syngas in an internal combustion engine, is highly questionable.
05. FEEDSTOCK FLEXIBILITY
Biomass gasification systems require relatively consistent feedstock properties, and are generally sensitive to changes in feedstock type, moisture content, ash content and particle size.
Drying is often necessary, and in the case of heterogeneous agricultural biomass, fuels will likely have to be pelletized. Pelletization increases fuel input costs dramatically and in most cases put project feasibility into question.
06. CAPEX/OPEX
The CAPEX figures quoted for biomass gasification plants by reputable Western suppliers are mostly well above the costs for ORC/combustion based plants. Several studies confirm that European biomass gasification plants entail higher investment costs per installed capacity.
Similarly, gasification plants from Asian suppliers when brought up to European equipment manufacturing standards, and in order to conform to emission limits will most likely exceed the costs for combustion/ORC based plants. Mostly designed and used for the electrification of areas with no grid access, biomass gasification systems promoted by Asian suppliers are far from conforming to the criteria set by investors and banks alike.
Similarly, OPEX figures are most likely to be significantly higher compared to a combustion/ORC based plant. As OPEX are practically a function of electricity produced, operational problems and frequent stops in plant operation for maintenance typically associated with biomass gasification plants will lead to higher operating costs even if fuel pelletization is not required,
07. GUARANTEES | BANKABILITY
In contrast to the performance and availability guarantees typically offered for combustion/ORC based plants, plant level guarantees for gasification are difficult to obtain.
Access to financing will most likely be equally problematic due to the high uncertainty surrounding gasification.