Difference between pinch and approach temperature in a boiler / hrsg

Pinch point: It is the difference in temperature of flue gas at evaporator outlet and water temperature at evaporator. The lesser the pinch point, more shall be evaporator surface area (as higher surface area would be required to absorb more heat from flue gas). The decision of pinch point should ideally be made keeping in mind overall costs and boiler efficiency.

Approach temperature: It is the difference in temperature between economiser outlet temperature and saturation temperature. Approach temperature should not be kept very less due to the possibility of steaming.

Types of cfbc boilers

From a neutral perspective following are the types of cfbc boilers:
a) Cold cyclone CFBC: Called as cold cyclone because cyclone temperature is "colder" (approx 400 Deg C) than a hot cyclone cfbc, which is because of some heating surfaces in the first pass. Aim is to have bed temperature at around 850 Deg C to aid in desulphurisation.

b) Hot cyclone CFBC: Heating surfaces in the second pass, hence cyclone is hotter.

c) Compact cyclone CFBC: Cyclone is part of pressure part circuit, done to reduce bed temperature.

d) U beam CFBC: U beams used instead of cyclone for filtering out coarse ash. Similar in nature as hot cyclone cfbc.

ASME Stamp

ASME Stamp is applied in shops of pressure parts, piping, valves, instruments in the water steam cycle path.
For a master stamp to be applied on hrsg/boiler it has to be ensured that the etection contractor is asme authorised. 
ASME stamp is generally accepted throughout the globe, with the notable substitutes being CE marking in Europe, GOST certification in Russia, IBR in India.

HRSG Harp

While working on HRSG for some years i one day thought why on earth is a HRSG pressure part called as harp.. and a simple google search gave me the answer, it is actually like a classical harp instrument!

Image Courtesy: Wikipedia