Читать книгу Mechanics of the Household - E. S. Keene - Страница 60

—Some types of boilers are made to burn soft coal with economy, with least work. Some types are made specially to burn the meaner grades of soft coal. Firing to prevent smoke is a source of economy and these ways of running should be followed—specially with large sectional boilers.

There are two types of soft coal, viz.: The free-burning coal, which breaks apart when burning, allowing the gases to freely escape; and the fusing-coking coal, which, when burning, first fuses into a solid burning mass with a hard crust over the top, slowly coking as it burns. The latter kind is most valuable for house-heating boilers because the gases are more thoroughly consumed. The fusing-coking coal is worth about 20 per cent. more for this purpose than the free-burning coal.

The gases should be allowed to pass off from the coal slowly. Leave air inlet on the feed door open if draft permits. If possible, use uniform sizes of coal. Avoid using coal having too much dust—the “run-of-the-mine” may be lower in price but its heat-making value is also low.

For the purpose of slow burning of soft coal, it is well in feeding at night to let the fire burn up freely so that the coals are very live with heat. Then fill in enough coal to last all night—leaving some of the live coals uncovered if possible. With large sectional boilers this exposure should be at the rear of the fire so that the flame will pass over the live coals. Thus the gases coming off from the fresh coal are burned and a larger amount of the full heat-producing value of soft coal is made use of and with less smoke.

After a boiler is so fed, the dampers (unless an automatic regulator is used) should be left about as follows:

Ash-pit draft damper open a little or closed, as draft may require.

Cold-air check damper open about one-eighth to one-third distance of the opening.

Smoke-pipe damper about one-half closed.

A little experiment with the draft will usually tell the operator the best way of leaving these dampers.

It will be found in the morning that the entire charge of coal is well burned or partly coked.

The coked fuel, or that which sticks together in a mass, should be broken up by the poker and more added generally as by rules given in other sections.

It must always be remembered that the soft coals mined in different parts of the country have widely varying heat-making capacities. To obtain satisfactory results brands must be selected which have an established reputation for excelling results in small boilers.