With coil type steam boiler, condensate cannot be recovered. Condensate contains 20% of the energy in steam.
Steam gives off its maximum heat when it condenses. This condensate contains close to 20% of the energy in steam. Recovering this condensate returns 20% of the energy back to the boiler. This way condensate recovery not only reduces the fuel bill but also reduces the water consumption.
When coil type boilers are being used as steam generators, because of the temperature limitation of the positive displacement pump, condensate return is not possible. Even if this were made possible the temperature limitation on the economizer prevents condensate recovery. Hence condensate is required to be drained. The loss due to this is equivalent to a loss of 9%-10% of total fuel consumption. Thus the plant would now consume fresh water equal to the steam demand on the plant. Additionally usage of this fresh water would have its associated treatment costs.
Even for steam loads as low as 700kg/hr, shell type boiler are available that not only deliver sustained high efficiency but also do not present any of the above limitations.
Assume a coil type FO fired boiler that caters to the 1tph steam demand of the plant. Because condensate cannot be returned in such boilers the condensate is drained locally. This leads to: