Engineering Thermodynamics
Producer gas is obtained by

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

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

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

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