[1] The Lurgi–Ruhrgas process was originally invented in the 1940s and further developed in the 1950s for a low-temperature liquefaction of lignite (brown coal).
The plant in Lincolnshire, the United Kingdom, operated in 1978–1979 with capacity of 900 tons of coal per day.
In late 1960s and early 1970s oil shales from different European countries and from the Green River Formation of Colorado, the United States, were tested at the Lurgi's pilot plant in Frankfurt.
In the 1970s, the technology was licensed to the Rio Blanco Shale Oil Project for construction of a modular retort in combination with the modified in situ process.
[2] The oil vapor and product gases pass through a hot cyclone for cleaning before sending to a condenser.
[3][7] The spent oil shale, still including residual carbon (char), is burnt at a lift pipe combustor to heat the process.