UPDRAFT GASIFIERS – Hot gas mode

HOT GAS MODE’ is the simplest and most efficient configuration for utilization of gasifiers for thermal (heating) applications. In this mode, the gas is exited from gasifier at such temperature that volatile constituents in gas (tars) remain in vapour form till the gas reaches the burner(s). To minimize condensation during transit, gas is conveyed through an insulated pipeline. Coarse dust particles are removed in preliminary dust catching equipment such as settlers and cyclones. Fine dust is difficult to remove and gets carried along with the gas. Water consumption is minimal in this mode. Despite removal of coarse particles and insulation of pipeline, small amounts of dust & tar continuously keep settling in the gas pipeline and passages. This requires to be cleaned periodically. Generally, online cleaning provisions are made to achieve uninterrupted long duration operation. Non-stop round-the-clock operations extending to 3-4 months are common in well designed ‘Hot Gas Mode’ gasifier configurations.

The energy content in hot gas (including sensible heat and energy of tar vapour) is of the order of 1450-1550 kcal/Nm3.
(After cooling & removing tar from the gas of ‘hot gas mode’ configuration, the measurable calorific value would report in the range of 1150 – 1250 kcal/Nm3)

The hot gas efficiencies are of the order of 80-85%. Higher flame / furnace temperatures are achieved with ‘hot gas’ as compared to that with ‘cold gas’.


ADVANTAGES & SUITABILITY

 Simple configuration, lower cost option
 Higher efficiency, higher flame temperatures
 Minimal water usage
 Water treatment issues do not arise
 Suitable to be used where gasifier can be close-coupled with utilization equipment (furnace, kiln, etc.), i.e when gasifier can be installed close to furnace / kiln and gas can be conveyed through a short pipeline</
 Suitable only when minor fine dust has no effect on quality of product being heated
 Suitable when fine controls are not required at individual burners, total gas quantity to a number of burners can be controlled
 
DISADVANTAGES & LIMITATIONS

 Frequent cleaning of pipelines and other gas passages is required (for which provision is made in the design)
 Frequent manual intervention is required for cleaning operations
 When gas is to be distributed through a long piping network, frequent cleaning becomes tedious
 Automatic control systems, requiring fine burner level controls, is not feasible