|High Value Products from Brown Coal|
|By Alan Chaffee, Professor and BCIA Fellow, School of Chemistry, Monash University|
|Victoria has enormous reserves of accessible and cheap brown coal. Victorian brown coal (VBC) is also exceptionally clean, in that it has low levels of nitrogen, sulphur, inorganic and mineral components by comparison with most other coals worldwide. This makes it very attractive as a hydrocarbon feedstock.|
|There are a number of current and many potential applications for VBC beyond power generation. VBC is currently used to manufacture briquettes for heating, a range of agricultural products and industrial char. Prior to the deployment of the Bass Strait oil and gas fields, VBC was gasified to provide town gas for Melbourne. Other prospective applications, although technically feasible, did not develop due to economic circumstances at the time; e.g. ‘coal dust’ for firing railway engines and coal-to-oil conversion.|
Given the recent escalation in crude oil and black coal prices, there is renewed interest in identifying alternative applications for VBC that can provide fresh commercial opportunities and economic activity for the state. High value products could be used domestically or exported.
One such application is the development of coke-like materials for metallurgical reduction of iron ore. As a result of increased global demand for iron and steel, the requirement for coking coal has also grown and it has become very expensive. Monash University, in collaboration with CSIRO, HRL Technology and Australian Char, is investigating whether VBC can be heated and chemically treated to make a coke-like product, which could be substituted for metallurgical coke (Figure 1) in a blast furnace.
There are two fundamental issues to address. First, the product must be hard and strong enough to support the column of iron ore that piles up on top of it in a blast furnace. Research has shown that the development of good mechanical strength in the product can be achieved, for example, by the addition of coal tar (Figure 2). Second, the
|Figure 1. Conventional metallurgical coke.|
|Figure 3. Surface functionalisation of a carbon surface enhances CO2 capture capacity and selectivity.|
|reactivity of the coke-like product must be controlled so that iron reduction occurs at the right temperature and over the right time frame in the blast furnace. Currently, VBC derived coke-like products are too reactive; hence reducing their reactivity is a priority for research.|
Another potential high-value application is the manufacture of active carbons from VBC. Active carbons have a very wide range of applications including water purification, sewerage treatment, groundwater remediation, air filtration, fuel storage, recovery of volatile organic compounds as well as medical applications. Work at Monash University, with collaboration from the University of Melbourne, Australian Char and the CRC for Greenhouse Gas Technologies, is focussed on the development of active carbons that can efficiently and selectively capture the carbon dioxide (CO2) emitted during coal and gas-fired electricity generation, so that it can then be sequestered to permanent storage. For best effect, the active carbons are modified by the addition of basic N groups at their surface. The basic groups can then interact with the slightly acidic carbon dioxide molecules.
Most adsorbents are regenerated (i.e., the adsorbed CO2 is removed) using heat (thermal swing) or vacuum (vacuum swing). Carbon adsorbents have an additional attribute, in that they are electrically conductive. Hence, if they can be fabricated into a monolith, they can be regenerated by the application of electrical current (electric swing).
These projects are supported with funding from Brown Coal Innovation Australia.
Figure 2. Experimental data showing how the addition of tar to VBC briquettes improves the compressive strength that develops in the coke-like product.
Figure 4. A carbon monolith (bottom) mounted into an electrical swing desorption unit. (This example is manufactured from an organic polymer).