Garg Lab Solutions

Coil type boilers are predominantly used as circulatory evaporators. They are used for vaporizing liquids by passing steam in the coils. Boilers are made by fusing no of parallel coils in the glass shell. Boilers coils are designed to provided bigger cross section in shell side as compared to condensers. The maximum permissible steam pressure at inlet in coil is 3 bars for boilers. This pressure can provide temperature of 1430°C with saturated steam. Higher temperature can be achieved by using suitable thermic fluid.

Following points should be taken in account while using coil type boilers.

• Flexible hoses should be used on coil inlet & outlet.

• Steam inlet line should be adequately trapped to avoid possibility of steam hammering.

• Start up by pass valve should be installed on coil outlet to clear the line of very heavy condensate flow produced on start up.

• Control valve & pressure gauge should be placed very near the steam inlet of the coil.

• Coil type boilers should not be fitted at bottom of columns or vessels as adequate circulation cannot be guaranteed in these locations.

• Boiler should be mounted in an external circulatory loop as shown in figure.

• Boilers can be mounted in series to provide larger heat tranGSer area.

• Preheated liquids should be used for better result in boilers.

• The steam pressure should always be adequate enough to ensure effective & smooth condensate removal. This pressure will vary on the size of boilers.

Performance Data
The maximum permissible steam pressure at the coil inlets of boilers is 3.0 bar.g. which is equivalent to a temperature of about 143�°C with saturated steam. Higher temperatures can be achieved by using heat tranGSer fluids.

The heat tranGSerred in most size can be considered on average as 400 W/m²K a steam pressure in the coils of 3.0 bar.g, although this figure declines marginally at lover pressure.

The table shows typical performances of boilers indicating the amount of water evaporated at atmospheric pressure with steam in the coils at various pressure.

Note : if the feed is cold, the performance of the boiler will be only about 85% of the figures quoted.