The gas treatment in the integrated bio SNG line-up comprises tar removal with the OLGA technology and sulphur and HCl removal with adsorbents.

OLGA tar removal

The OLGA process is based on applying an organic scrubbing liquid (i.e. “OLGA” is the Dutch acronym for oil-based gas washer). The advantages of the OLGA tar removal technology, compared to alternative conventional tar removal approaches, can be summarised as [1]:

• Tar dewpoint of clean product gas is below temperature of application, therefore there is no condensation of tars in system;
• No fouling of the system resulting in increased system reliability and higher availability;
• Tars are removed prior to water condensation to prevent pollution of process water;
• Tars are recycled to gasifier and destructed avoiding the handling of problematic (and expensive) tar waste streams;
• Tar recycling increases the overall efficiency of the process
• Scalable technology allowing the application from lab to commercial scales.

It is assumed that the OLGA is operated downstream a high-efficient solids removal step (e.g. a hot gas filter). The OLGA gas inlet temperature has to be kept higher than the tar dewpoint (typically > 400°C)), similarly the gas outlet temperature must be higher than the water dewpoint (typically 60-80°C).

In the first OLGA column (‘Collector’) the product gas is cooled, upon which the liquid tars are collected. Also dust particles that were not removed by the upstream cyclone are collected. In the second column (‘Absorber’) gaseous tars are absorbed in the scrubbing liquid at the resulting temperature. The liquid tars are separated from the scrubbing liquid and returned to the gasifier; also a small amount of the scrubbing liquid is bleed and recycled to the gasifier. For the absorption step, scrubbing columns were selected that are interacting with each other in a classical absorption-regeneration mode. The scrubbing oil from the Absorber with the dissolved tars is regenerated in the ‘Stripper’. Air is used to strip the tars from the scrubbing oil and the tar-loaded air is used in the combustor of the MILENA. The loss of scrubbing liquid in the Stripper by volatilisation is minimised by use of a condenser.

The cleaned product gas leaving the Absorber is “tar-free” (i.e. free of tar related problems) and can be treated further in the water-based gas cleaning, fired in a gas engine, or used for more advanced catalytic applications.

Development and optimisation of the OLGA process was not part of the project. Details on OLGA can be found in references [1] and [2]. Application of OLGA in integrated systems with catalytic synthesis is described in reference [3].

Gas cleaning

Gas cleaning is performed either by water scrubbing in combination with guard bed or absorbent materials, depending on the selected system concept. Results of a system including a water scrubber are described in reference [3]. Development of a gas cleaning line-up based on absorbents and which is operated at elevated temperatures (i.e. at least above the water dewpoint) was carried out in a parallel project. Results are described in the final report of this project [4].

References: 

1. H. Boerrigter, S.V.B. van Paasen, P.C.A. Bergman, J.W. Könemann, R. Emmen and A. Wijnands: "OLGA" tar removal technology. ECN, ECN-C--05-009, 2005, The Netherlands.

2. H. Boerrigter, S.B.V. van Paasen, P.C.A. Bergman, J.W. Könemann and R. Emmen: Tar removal from biomass product gas; development and optimisation of the OLGA tar removal technology.  In the proceedings of the 14th European Biomass Conference & Exhibition, 17-21 October 2005, Paris, France.

3. H Boerrigter, H.P. Calis, D.J. Slort, H. Bodenstaff, A.J. Kaandorp, H. den Uil and L.P.L.M. Rabou: Gas cleaning for integrated biomass gasification (BG) and Fischer-Tropsch (FT) systems. ECN, ECN-CX--04-004, 2004, The Netherlands (confidential).

4. S.V.B. van Paasen, M.K. Cieplik and N.P. Phokawat: Gasification of non-woody biomass - Chlorine and Sulphur removal; economical and technical perspectives. ECN, ECN-CX--06-080. 2006, The Netherlands (confidential).