The development of a draft protocol for the sampling and analysis of particulate and organic contaminants in the gas from small biomass gasifiers

Abstract

A number of companies have developed, and are developing, power generation technology based on the gasification of biomass. These technologies have three process steps: the gasification reactor, cleaning of the producer gas, and an engine generator set. The producer gas from all gasification reactors contains particulates and organic contaminants (tars) which, if not removed, would damage the engine or incur an unacceptable level of maintenance. The efficiency of the gas cleaning step is therefore fundamental to the successful operation of this technology. A number of different sampling and analysis methods have been used by manufacturers and other workers in this field to determine the level of particulates and organic contaminants in the gas exiting the gas cleaning system. This diversity of methods makes the comparison of operating data from different sources very difficult. This represents a significant barrier to the further development and commercialisation of the technology. The members of the Gasification Task of the IEA Bioenergy Agreement, the US DoE and DGXVII of the European Commission have been aware of this barrier for some time. To address it they called a joint meeting in Brussels, Spring 1998, where it was decided to develop two sampling and analysis protocols that could be used as reference methods for further work. One protocol would be used for small scale, fixed bed, engine based systems and the other for larger utility scale plant. The meeting delegated the preparation of the protocols to two working groups, one for each scale of operation. The goal is for these groups to progress the two protocols within a short time to a status that is sufficiently developed to enable work to start on the preparation of US and EU standards. This report details the initial discussions and conclusions reached by the working group for the small scale protocol. In principle, the group decided that a method similar to that used for sampling PAHs in stack gas would be appropriate. The main elements of the system would be an isokinetic probe for sample extraction, a heated filter for particulate collection, a water condenser and a series of impingers, containing cooled solvent to collect the organic contaminants. The group felt that the method should include both gravimetric and chromatographic determinations of the concentration of organic contaminants. Dichloromethane was selected by the group as the solvent that would be used for all aspects of the method. However, at this stage, there remains some uncertainty over this selection. To resolve this and other uncertainties a programme of work is described that will progress the protocol to a stage where procedures could be started to adopt it as a European and US standard. The report is structured in three sections. Section 1, the Working Group Report, documents the discussions of the working group and wider meeting. Section 2 is a draft protocol. The protocol is necessarily in a preliminary form at present but will be updated successively as a result of further work and consultations. Section 3 contains calculations for typical equipment items and procedures.