Engineering Thermodynamics
Producer gas is obtained by

Passing steam over incandescent coke
Carbonization of bituminous coal
Partial combustion of coal, coke, anthracite coal or charcoal in a mixed air steam blast
Passing air and a large amount of steam over waste coal at about 650°C

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Engineering Thermodynamics
In order that a cycle be reversible, following must be satisfied

When heat is being absorbed, temperature of hot source and working substance should be same
Free expansion or friction resisted expansion/compression process should not be encountered
All of these
When beat is being rejected, temperature of cold source and working substance should be same

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