$7.$ Detail the Lurgi process for coal gasification. Discuss its operation, advantages, and the quality of gas produced.

$8.$ Describe the Winkler process for coal gasification. How does it differ from the Lurgi process in terms of technology and application?

$9.$ Explain the KopperTotzek process for coal gasification. What distinguishes it from other gasification processes, and what are its main advantages?

$10.$ Discuss the importance of liquefaction in the context of solid fuels. How does this process transform coal into a more versatile and usable form of energy?