Transparent Make

Other Make

• All tubes in evaporator are risers. Separate down-comers are provided outside the heating zone. Cross sectional area for flow in riser is more resulting in much better natural circulation. Since the down-comers are not heated at all, The termo-syphon effect is many times better than bi-drum design where both risers & down-comers are heated. The only difference is the heat gained is different.

• Some tubes in evaporator are riser & balance are Down-comers. No separate down-comers are provided outside the heating surface. Cross sectional area available for circulation is less compared to single-drum design. In addition to this, the density difference in risers down-comers is much less since both are heated. This results into lower circulation rate compared to ‘Transparent’ design.

• The evaporator consists of No. of panels (cassettes) connected to riser & down-commer header. These headers are in turn connected to drum. Hence it is not necessary to replace many tubes if only one tube leaks. Individual panel (Cassette) can be taken outside for repairs. Repairs are quick & economical.

• All tubes are directly expanded in the drum. Even if one tube at center portion leaks, huge No. of tubes need to be replaced since it is necessary to remove these tubes even to access the leaked tube. These repairs consume lot of time & money.

• What – ever soot does not get pneumatically conveyed to chimney it has a space at bottom. It does not occupy area on heating surface.

• What- ever soot does not get pneumatically conveyed to chimney, gets accumulated on top of bottom drum where all tubes are connected to drum. This makes it very difficult to clean this soot manually during annual shut-down.

• Tubes are placed vertically with axes parallel to gas flow. It does not obstruct the flow of gas. Possibilities of soot accumulation are less since vertical downward flow of flue gas will help in dislodging the soot particles.

• Tubes are placed vertically with their axes perpendicular to flow of gas. This results into obstruction to gas flow & soot particles are arrested.