Classification of Gasifiers

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The direction of the air flows gives us DownDraft (DD), and UpDraft (UD) and CrossDraft (CD).  In all three the fire is at the bottom.  There is also a "Top-Lit UpDraft" (TLUD) gasifier.  AVUD is a type of traditional UpDraft, but it is "Another Variation" specific for micro-gasification.

The purpose and the cleanliness of the gases give us gasifiers for heat only (with burning the tars as in TLUDs and AVUDs) and for power as in the operation of internal combustion (IC) engines that can spin electricity generators or move vehicles or turn pumps (with gases either created without tars or with the tars removed as in large DD gasifiers). CHP (Combined Heat and Power) means that after the electro-mechanical power is made, the remaining heat is put to some use.

Sizes of gasifiers are in relative terms with rather overlapping categories. Confusion can occur because "energy" can be electrical (kWe), mechanical (HP), or thermal (kWth or BTU), or megaJoules, etc... "Power" is energy per specified unit of time. Energy should be expressed as "per hour" to show the power concentration, and kilowatts of electrical output is really kwe-hr.

NOTE: 

• Large (also Super or Mega or other terms) is usually with hundreds of megawatts of electricity and thousands of megajoules or millions of BTU, etc.
• Medium seems to be seldom used as a descriptor.
• Small for the CHP gasifiers with gensets for electricity (such as 30 to 80 kilowatts of electricity.- 30 to 80 kwe) can be substantial for the thermal-only units measured in kwth, such as 500 kwth (1.7 million BTU) and larger.
• Mini is a term not used, but might cover the sizes from 100 kwth (350 k BTU up to 500 kwth (1.7 k BTU).
• Micro is a quite new term.
  • The larger sizes of micro-gasifiers are in the 15 to 100 kwth range (50 k to 350 k BTU), the sizes of the Chip Energy furnaces.
  • The middle sizes of micro-gasifiers could be with 6 to 15 kwth (20 k to 50 k BTU), like substantial outdoor grills for American homes and for the Chip Energy Biomass grills.
  • The small end of micro-gasifiers includes the cookstoves producing 1 to 6 kwth (3 k to 20 k BTU) for a one or two pot stove. TLUD (Top-Lit UpDraft) gasifiers have many advantages in this size and purpose.