Handbook for Methane Control in Mining - AMMSA

10Figure 1–4.—Estimated methane content of coalversus depth and rank. Values shown are an upper limit.differences in coalbed depth, differencesin production rate, and geological anomalies12 such as faults. Some of these correctionsare simple, if inexact. 13When no other mine is nearby, a veryrough emission forecast for the entiremine may be obtained using the gascontent of the coal. For example, Saghafiet al. [1997] have reported the relationshipbetween gas content and mine emissionfor Australian mines (Figure 1–5). Theamount of methane released from the mineexceeded the methane in the mined coalby a factor of 4. This differs from theresults of Kissell et al. [1973], whomeasured a factor of about 7 for someU.S. mines. The difference is probablydue to methane emissions from adjacentcoalbeds and porous rock. Other associationsbetween mine emission and gascontent have been made without usingproduction data. Grau and LaScola [1984]have correlated the mine emission of some U.S. mines in cubic feet per day with the in situ gascontent in cubic feet per ton. 14Much more on forecasting for coal mines is covered in thecoal mine forecasting chapter (Chapter 8). Forecastingfor metal and nonmetal mines is covered in this section.Forecasting for tunnels is covered in the tunneling chapter(Chapter 14).12 The effect of geological anomalies is discussed in Chapter 7.13 Sometimes very inexact. For example, the methane emission can be assumed as roughly proportional to depth.However, Diamond and Garcia [1999] compared the methane emission rates of two longwall panels a mile apart.The second panel was 37% deeper than the first, but gave 61% higher emissions. The emissions were much higherbecause the elapsed time between development of the panel and retreat of the longwall face was much less in thesecond panel. Thus, there was less time for the second panel to drain gas into the returns, so when it was mined theemission was higher than expected.14 Grau and LaScola report 1980 mine emission data. Reliable U.S. data after 1980 are not available. As degasificationprograms became widespread, the degas quantities were retained as confidential information by coal companies.