OLGA tar removal

OLGA is an advanced scrubbing technology for tar removal downstream gasification processes. Its basic idea is to remove tars above the water dew point, so that mixtures of tar and water are avoided. OLGA tar removal prevents issues with fouling, water pollution, and coking (in case of downstream catalytic processes). The OLGA technology is developed and patented by ECN and is licensed to Dahlman.

OLGA in the system

OLGA generally is placed close to the gasifier. The temperature of the gas entering OLGA needs to be above the tar dew point and typically is 300-500°C. Tars and particles are removed in two steps. The exit temperature is above the water dew point, typically 70-100°C. A cyclone is preferred upstream OLGA to remove the majority of the particles. The general system therefore consists of gasifier, gas cooler, cyclone, OLGA followed by additional equipment depending on the gas application and/or emission limits.

OLGA benefits

There are many reasons to include OLGA in a gasification system. It is a key process which can be applied in all kind of different systems.

OLGA removes:

• condensable tars (e.g. tar dew point reduces from 450° to under 20°C)
• particles
• light tars (e.g. naphthalene)
• dioxins
• large organic sulphur compounds such as di-benzothiophene

OLGA does not remove:

• benzene and toluene (or only partly)
• methane and ethylene and other small hydrocarbons
• other small molecules such as H₂, CO, CO₂, HCl, H₂S, …

OLGA is flexible:

• can treat gases with high tar concentrations, tested up to 50 g/nm3
• can be up-scaled to 30 000 nm3/h (designed) or even larger
• can be coupled to fluidized bed gasifiers, fixed bed gasifiers, and more
• can be coupled to gasifiers operating on wood, manure, RDF, etc.
• separated tars can be recycled to the gasifier
• can be used in systems to produce power, heat, SNG (Substitute Natural Gas), chemicals, and biofuels

The OLGA technology

OLGA consists of two steps. In the so-called collector, the gas is cooled from well above the tar dew point (often 300-500°C) to just above the water dew point (70-100°C). Tars condense and are separated together with a large fraction of the particles. The heat of cooling comes available through hot oil as medium-temperature heat. The second step consists of a more conventional absorber reactor where lighter tars are removed. Between the collector and absorber, a wet ESP (Electrostatic Precipitator) takes care that all particles and aerosols are separated.

Scheme of the OLGA tar removal technology

Status

ECN started the development of OLGA around the year 2000. A lab-scale OLGA facility (2 nm3/h) and a pilot-scale OLGA facility (200 nm3/h) are available at the premises of ECN. Both are connected to a gasifier operating at all kind of fuels that can produce gas of various quality.

Dahlman as the supplier of the OLGA-technology has supplied two OLGA systems so far to outside-ECN customers. The French OLGA is connected to a fixed bed updraft gasifier and it treats approximately 2000 nm3/h. The Portuguese plant is operated on approximately 2000 nm3/h from a fluidized bed gasifier operating on chicken manure. Both plants are CHP producing approximately 1 MWth.

Developments

OLGA is a commercially available technology supplied by our partner Dahlman. ECN still owns and operates two test facilities that are used to support the work of Dahlman. This includes testing new combinations like gasification of new wastes/fuels or operating at different gasifier conditions to simulate a specific gasification technology. It also includes supporting Dahlman with in-house models, both on gasification behavior as well as OLGA performance. It also concerns different back-end processes such as the production of Substitute Natural Gas (bioSNG: link naar bioSNG) where the tar-free gas leaving OLGA should fit the downstream equipment’s specifications. 

More information

• A paper by Rabou describes the history of the OLGA development, the failures and successes of previous attempts and the status as of 2009: Energy Fuels 2009, 23, pp. 6189–6198.
• A more general overview on producer gas cleaning can be found on: http://www.ecn.nl/docs/library/report/2008/e08078.pdf.
• A paper focusing on the flexibility of OLGA can be found at: http://www.ecn.nl/docs/library/report/2009/m09120.pdf.
• If tar concentrations and composition is known (link naar gas analysis), the tar dew point can be calculated. A simple model is available from our website (link naar www.thersites.nl).