To permit partial load operation, a control arrangement is provided to effect, in dependence upon an operating load of the boiler, control of at least one of the flow rate of the combustion air into the boiler, and {HEAD ~ the operating pressure} in {TAIL ~ the combustion chamber} of the boiler 
To permit partial load operation , a control arrangement is provided to effect , in dependence upon an operating load of the boiler , control of at least one of the flow rate of the combustion air into the boiler , and { HEAD ~ the operating pressure } in { TAIL ~ the combustion chamber } of the boiler
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