Lignite should be used as a soil conditioner, to produce humic and fulvic acid, and in animal farming.
According to a news article in Daily Times, Pakistan has the seventh largest coal reserves in the world with over 186 billion tonnes of coal. It further adds with reference to Lahore Chamber of Commerce and Industry (LCCI) that, “most of the world’s lignite coal is found in Asia and Pakistan tops in lignite coal-bearing countries as 97 percent of coal reserves of Pakistan belong to lignite and remaining only 3.0 percent are sub-bituminous to bituminous”. According to these sources, 99.6% of the total coal reserves (186 billion tons) are found in Sindh and only 0.4% in the remaining country including Kashmir. Thus Pakistan can boast a hidden asset of lignite amounting to at least 180 billion tons. According to some estimates by Geological Survey of Pakistan (GSP), Pakistan is at number 7 in the list of top 20 countries of the world after the discovery of huge lignite coal resources in Sindh, and one of the world’s largest lignite deposits spread over more than 9,000 km2. Understandably, this reserve can meet the country’s fuel requirements for centuries. There is however, a catch in this suggestion.
Lignite (brownish-black in colour and termed as brown coal) is considered to be a low-rank coal that has;
- A heating value of less than 20 MJ/kg as compared to >30 MJ/kg for a good quality bituminous coal,
- Fly ash with high electrical resistivity, making it difficult to collect in electrostatic precipitators,
- Mineral matter that is largely organically bound and inseparable by standard washing techniques,
- High sodium content that contributes to boiler fouling and slagging problems, and
- Quartz content that accelerates erosion of furnace burners.
In spite of the negative attributes of lignite as a source of energy, Engro Corporation has entered into an ambitious agreement with Government of Sindh to use Thar coal (97% lignite) for generating 3960 MW electricity; 660 MW to be generated by end 2017. This decision was taken perhaps because of lignite’s high reactivity (which is due in part to high oxygen content) making it amendable to use in a rather coarse form compared to higher-rank coal that requires fine grinding to ensure complete combustion in pulverised coal systems. High reactivity of lignite together with low-sulphur content and non-caking properties make it suitable for gasification and liquefaction.
Whether or not lignite is suitable for use as energy source, it is still recognized as a highly valuable soil conditioner for improving soil properties and enhancing crop yields. During the process of formation (Fig. 1), including temperature and pressure, microorganisms seemed to have played an important role in the chemical configuration of lignite (peat being the precursor) at least during the early years of burial of biomass. Both aerobic and anaerobic microbes are thought to be involved in the process. Gelification of biomass (mostly of gymnosperms, although contribution of angiosperms has also been suggested based on the evidence gathered through state-of-the-art analytical methodologies) would appear to be mediated mainly by aerobic microbes. The particular configuration of lignite that entails preservation of oxygen-containing functional groups like OH and COOH gives this poor quality coal a unique feature of physiological functionality when treated with hydroxide of ammonium, potassium or sodium. The resulting water soluble entities i.e. humates (humic acid and fulvic acid) have now been unequivocally established as having an immense impact on physiological functioning of plants and animals alike. Humates released from lignite in soluble forms have multiple benefits when applied to soil and plants or fed to animals as food supplement. Over past few decades, humates have attained a key position in agricultural formulations and are being increasingly recognized as metabolic enhancers in animals as well.
Simplest way to use lignite in agriculture would be as a soil amendment. Roughly ground lignite can be incorporated into soil where it will serve as a sustainable source of humates. It is fairly well established now that micro-site changes in pH do occur in soil. The pH may increase or decrease depending upon multiple factors. It is known, however, that pH increases following hydrolysis of urea (most common nitrogenous fertilizer in Pakistan). The ammonium thus formed is susceptible to volatilization loss at elevated pH thereby incurring economic losses (40-50% of urea nitrogen may be lost from the soil plant system) as well as environmental implications. Elevated pH not only induces ammonia volatilization losses but could lead to precipitation and non-availability to plants of fertilizer phosphorus. Lignite can help mitigate both the negative processes. It will absorb/sequester ammonia (humates contained in lignite will react with ammonia) thereby having a stabilizing effect on soil pH and prevention of ammonia volatilization and phosphorus precipitation (both occur at high pH induced by urea hydrolysis). On the long-run as well, the process of ammonification of organic matter in soil does release ammonia and therefore lignite will have a sustained positive impact on soil pH. It is not only the soil pH, but humates released in soluble forms following interaction of ammonia with lignite, will have multiple benefits to crop growth as mentioned earlier.
In view of above, it is suggested that lignite reserved in the country be exploited for the following:
- A soil conditioner.
- Production of humic acid and fulvic acid (simplified process is shown in the picture) for domestic use (at subsidized rates) and exports.
- Use in animal (poultry and others) farming as part of bedding as well as fodder supplement; Farmyard manure thus produced (bedding + droppings) will be a high value soil additive. In these systems, lignite will also serve as ammonia scavenger.
It is envisaged that lignite will help make agriculture more environment-friendly and profitable on a long term basis. Government of Pakistan will do well establish a mega-facility for processing lignite at Thar coal fields.