That question is pretty broadly phrased, and in some respects, the answer depends on what perspective the question is asked from. Such as what country you are in (i.e., standard of construction, jurisdictional laws), and the potential applications that are being considered, such as power generation, petroleum or chemical processing, waste heat applications, steam versus other thermal fluid, or water, etc.
A bit more specificity might make it easier to answer the question that you pose.
__________________
"We have met the enemy, and he am us" - Pogo
sir,I belong to india and i want to Know boilers classification according to steam pressure and its different working pressure. kindly guide me These boilers are for power generation.
First, "Low Pressure" and "High Pressure" are very relative terms.
In the US, a low pressure steam boiler is one that operates at or below 15 PSIG, or 2 bar, absolute, with a corresponding temperature of 250 degrees F / 121.11 C / 394.26 K. Anything in excess of these pressures and temperatures would be termed "High Pressure", which dictates the construction standard to which it must be built (ASME Section I - Power Boilers).
In the context of your question, and as your original subject made reference to cfbc (Circulating Fluidized Bed Combustion) boilers, the pressure at which various generating units operate varies greatly, but new construction would tend to lean towards designs for "Super Critical" pressures/temperatures.
The "Critical" temperature of a fluid is that temperature at which the fluid cannot exist in its vapor phase, regardless of pressure applied. In terms of the thermal properties of water, that temperature is 705 degrees F / 373 C / 647 K, with a corresponding saturation pressure of 3199 PSIG / 22 Mpa / 220.6 Bar. At that threshold, there is no clear interface between vapor and liquid.
Any steam generator operating at or above that threshold would be termed "Super Critical", and those operating below it would be termed "Sub Critical".
As far as the fluidized bed technology, there is an excellent technical paper by S.J. Goidich of Foster Wheeler that can be found at the following link;
cfbc boilers
Re: cfbc boilers
