The coal industry has looked long and hard for the Midas touch that could convert low rank coals into higher value bituminous equivalent products. Many have tried, but few have succeeded and none have yet been fully commercialised. A summary of a few current options was published in the April 2012 issue of World Coal.1
Many of these alternative coal beneficiation technologies involve the use of high temperatures, high-pressure vessels or chemical processing to remove the moisture from low rank coals. Most are complex processes that are expensive to operate, involving methods that often drive off valuable volatile matter, leaving a product that is friable and susceptible to moisture re-absorption, as well as spontaneous combustion.
Over the last couple of months, a number of announcements have surfaced regarding coal beneficiation technologies entering the commercial demonstration stage. These include advances in microwave drying, pelletising and flash drying techniques. While each has its individual potential merits, all appear to remain expensive, complex options and all must overcome the development, scale-up and commercial deployment hurdles that numerous previous attempts have failed to clear.
Among these announcements, however, it is noteworthy that GTL Energy Ltd (GTLE) has recently achieved a major milestone in commissioning and operating a coal drying and briquetting plant in New Zealand, which provides the operating platform to demonstrate their technology at a commercial scale.
Benefits of coal drying
Globally, there is an abundance of low rank coals that contain 20 – 70% water by weight. This water volume reduces the calorific value of the coal causing it to burn less efficiently. This, in turn, requires larger and more expensive power plant designs, creating more emissions per unit of energy produced relative to higher rank coals. As a consequence, low rank coals are worth much less on a US$/t basis. The price arbitrage between low rank and high rank coals provides an opportunity for coal drying to add demonstrable value to low rank coals. This is especially true in Asian markets, which are highly affected by Chinese and Indian demand, as well as the supply side dynamics from Indonesia, Australia and the US. The availability of surface mineable, high quality bituminous coal is lagging behind this growing demand, meaning that miners are forced to move towards either higher cost underground bituminous reserves, high grade coals with high sulfur and ash, or lower calorific value sub-bituminous and lignite coals.
Further exacerbating the situation, the Indonesian Government has been considering a restriction on the export of low rank coal. Earlier this year, the Chinese Government proposed a ban on the import of coal with calorific values below 4540 kcal/kg NAR (roughly 5000 kcal/kg GAR). While still under discussion, either could potentially eliminate a significant quantity of Indonesian coal from this attractive and rapidly growing market.
Figure 1 shows how coal drying technology, like that developed by GTLE, could significantly increase the value of low grade Indonesian coals. In this case, three low calorific value coals listed on the Indonesian Ministry of Energy and Mineral Resources’ pricing list (the HPB list) have been selected. This chart shows the price trend-line for the Indonesian HPB marker coals, as well as how the low calorific value coals fall roughly US$ 10 below this trend-line.
It also demonstrates how coal drying would lift the calorific value content for these three coals above the minimum level required under the proposed China regulation and significantly increase their value. Looking over the last 4 years of HPB pricing data (Figure 2), the average price spread between the LIM 3000 and Envirocoal 5000 products was approximately US$ 46/t.
With global pressure growing on utilities to reduce CO2 and other harmful emissions, low rank coals are finding it increasingly difficult to be competitive on an efficiency and environmental basis. Furthermore, export of low rank coals tend to be challenged by high fines content, oxidation and reactivity.
GTLE recently commissioned studies by the Electric Power Research Institute and the engineering firm Black and Veatch (B&V) to evaluate the difference in both capital and operating costs along with the associated emissions output for a new power plant using a low rank Indonesian coal (3500 kcal/kg) compared to one using that same coal after being upgraded using the GTLE beneficiation technology (5500 kcal/kg).
From a capital cost perspective, a 750 MW power plant designed to burn the upgraded coal was estimated to cost approximately US$ 124 million less than a unit designed for the lower rank alternative due to savings in the size of boilers and associated equipment, a 13% reduction. Additionally, from an operating cost perspective, the upgraded coal would reduce the fuel-related expenses by over US$ 0.008/kWh or 12.5%, due to:
- Annual coal throughput reduced by 48% (a combination of efficiency gains and less tonnage with a higher calorific value).
- Fly and bottom ash disposal reduced 13%.
- Annual SO2 emissions reduced 8%.
- Annual direct maintenance costs reduced 22%.
B&V also looked at the full-cycle CO2 emissions from the coal drying and the power plant combined, confirming that an overall reduction of 2.5 – 5% was a realistic expectation.
Test burns of GTLE upgraded briquettes have been completed in both a pilot-scale environment at research facilities in the US and Australia, as well as in one commercial power plant in the US. Results from all of these tests have confirmed the ease of handling and the relative benefits of burning these upgraded coals vis-à-vis their raw equivalents.
The markets will need to continue to look for higher efficiency coals. There is significant economic and environmental incentives for low rank coal producers to look at coal beneficiation as a way to participate competitively in these growing markets.
1. DONG, N., “Trading up”, World Coal (April 2012), pp. 20 – 24.
Written by Claude C. Corkadel.
Read the article online at: https://www.worldcoal.com/coal/23122013/coal_drying_commercialisation_part_1/