Flash steam
There are a number of principal considerations
when connecting a biomass system to an existing
or planned heating system. Most heating systems
are designed to operate at 82 °C flow, 71 °C return,
to avoid producing steam in the heating system
in the event of a sudden system depressurisation
or system overheating. This is a major safety
consideration. Steam, known as flash steam, will
form in a system pressurised to more than 1 bar if
the system depressurises rapidly3. The operating
pressure will be well over 1 bar even in systems
pressurised by a gravity header tank. By holding
the design operating temperature down to 82 °C,
a flash margin of 18 °C is provided so that flash
steam cannot be produced. However, to maximise
the thermal storage capacity of a buffer tank it is
better to operate the biomass system at up to 95 °C
and where possible to design the heating circuits to
return at a temperature lower than 71 °C.