Ground-breaking Net Efficiency
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A strength of the HTCW process over other gasifiers, particularly lower temperature air blown plants, is the clean low tar nature of the syngas. This allows better optimisation of the engines and improvements in their reliability and durability. Part of the air-blown gasification industry has responded to this challenge by the introduction of Plasma assisted gasifiers.
How Plasma Gasification Works
Plasma assisted gasifiers can remove tars etc with the same effectiveness as the HTCW, but the inefficiency associated with heating the inert nitrogen in the air obviously remains. Plasma gasifiers normally operate as two stage operations: the first stage is a conventional air blown gasifier. The dirty syngas from this unit passes into a separate chamber containing an electrically powered plasma torch and additional air is added and the torch raises the temperature. A tar free gas can be produced. The final syngas has a low CV typical of air blown units.
is typical. Simply put, to express the net process efficiency, this power needs to be subtracted from the gross amount of energy contained in the input feed material (= the waste). This reduces the process efficiency further, resulting in significant lower profitability.
Demanding HTCW Efficiency Standard
Overall Nett Process Efficiency % =100 x Total Electrical Power Generated — Electrical Power Consumed By Entire Process (MW) + Total Heat Sold To Customers (MW). This is divided by : Total Energy In All Feeds (MW).
Tar Free Gas
The engine and generator, together with the heat recovery plant, are in fact conventional equipment. The engines need to be adjusted to suit the syn-gas. The HTCW produced syn-gas has a calorific value normally greater than 9 MJ / M3, almost twice that of an air blown gasifier. The improved CV and the tar-free nature of the gas allow improved combustion and, arguably, lower wear and tear on the engine generator equipment, compared to syn-gas formed by air blown gasifiers.
Efficiency vs Calorific Value
The efficiency of any gasification process is always a function of the CV of the feed. Below is a comparison of the electrical efficiency of an HTCW to that of an air blown plasma unit.
Good use of HTCW internal heat will increase the net electrical efficiency by at least another 10% than shown below. This, together with the illustration on the next page, shows HTCW superiority in generating higher energy yields than incinerators / air blown gasifiers, as the CV ratio rises.
In this illustration wood is considered as the fuel and the moisture content is altered to vary the CV of the waste. The HTCW is operating at 1400C, the oxygen is assumed to have been supplied as liquid. The Plasma operates at 1050C and the plasma torch power is 0.4 MWh/t of feed.
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