Steam, Its Generation and Use Part 38

(D) Equivalent evaporation.

(E) Heat balance.

(F) Total heat of combustion of coal.

(G) Air for combustion and the methods recommended for calculating these results are in accordance with those described in different portions of this book.

16. DATA AND RESULTS

The data and results should be reported in accordance with either the short form or the complete form, adding lines for data not provided for, or omitting those not required, as may conform to the object in view.

17. CHART

In trials having for an object the determination and exposition of the complete boiler performance, the entire log of readings and data should be plotted on a chart and represented graphically.

18. TESTS WITH OIL AND GAS FUELS

Tests of boilers using oil or gas for fuel should accord with the rules here given, excepting as they are varied to conform to the particular characteristics of the fuel. The duration in such cases may be reduced, and the "flying" method of starting and stopping employed.

The table of data and results should contain items stating character of furnace and burner, quality and composition of oil or gas, temperature of oil, pressure of steam used for vaporizing and quant.i.ty of steam used for both vaporizing and for heating.

TABLE DATA AND RESULTS OF EVAPORATIVE TEST SHORT FORM, CODE OF 1912

1 Test of.................boiler located at................................

to determine...............conducted by..............................

2 Kind of furnace..........................................................

3 Grate surface.................................................square feet 4 Water-heating surface.........................................square feet 5 Superheating surface..........................................square feet 6 Date.....................................................................

7 Duration............................................................hours 8 Kind and size of coal....................................................

AVERAGE PRESSURES, TEMPERATURES, ETC.

9 Steam pressure by gauge............................................pounds 10 Temperature of feed water entering boiler.........................degrees 11 Temperature of escaping gases leaving boiler......................degrees 12 Force of draft between damper and boiler...........................inches 13 Percentage of moisture in steam, or number degrees of superheating..................per cent or degrees

TOTAL QUANt.i.tIES

14 Weight of coal as fired[72]........................................pounds 15 Percentage of moisture in coal...................................per cent 16 Total weight of dry coal consumed..................................pounds 17 Total ash and refuse...............................................pounds 18 Percentage of ash and refuse in dry coal.........................per cent 19 Total weight of water fed to the boiler[73]........................pounds 20 Total water evaporated, corrected for moisture in steam............pounds 21 Total equivalent evaporation from and at 212 degrees...............pounds

HOURLY QUANt.i.tIES AND RATES

22 Dry coal consumed per hour.........................................pounds 23 Dry coal per square feet of grate surface per hour.................pounds 24 Water evaporated per hour corrected for quality of steam...........pounds 25 Equivalent evaporation per hour from and at 212 degrees............pounds 26 Equivalent evaporation per hour from and at 212 degrees per square foot of water-heating surface........................pounds

CAPACITY

27 Evaporation per hour from and at 212 degrees (same as Line 25).....pounds 28 Boiler horse power developed (Item 2734).............boiler horse power 29 Rated capacity, in evaporation from and at 212 degrees per hour....pounds 30 Rated boiler horse power...............................boiler horse power 31 Percentage of rated capacity developed...........................per cent

ECONOMY RESULTS

32 Water fed per pound of coal fired (Item 19Item 14)................pounds 33 Water evaporated per pound of dry coal (Item 20Item 16)...........pounds 34 Equivalent evaporation from and at 212 degrees per pound of dry coal (Item 21Item 16)...................................pounds 35 Equivalent evaporation from and at 212 degrees per pound of combustible [Item 21(Item 16-Item 17)]......................pounds

EFFICIENCY

36 Calorific value of one pound of dry coal.........................B. t. u.

37 Calorific value of one pound of combustible......................B. t. u.

( Item 34970.4) 38 Efficiency of boiler, furnace and grate (100 -------------)....per cent ( Item 36 )

( Item 35970.4) 39 Efficiency of boiler and furnace (100 -------------)...........per cent ( Item 37 )

COST OF EVAPORATION

40 Cost of coal per ton of......pounds delivered in boiler room......dollars 41 Cost of coal required for evaporating 1000 pounds of water from and at 212 degrees........................................dollars

[Ill.u.s.tration: Portion of 3600 Horse-power Installation of Babc.o.c.k & Wilc.o.x Boilers, Equipped with Babc.o.c.k & Wilc.o.x Chain Grate Stokers at the Loomis Street Plant of the Peoples Gas Light & c.o.ke Co., Chicago, Ill. This Company has Installed 7780 Horse Power of Babc.o.c.k & Wilc.o.x Boilers]

THE SELECTION OF BOILERS WITH A CONSIDERATION OF THE FACTORS DETERMINING SUCH SELECTION

The selection of steam boilers is a matter to which the most careful thought and attention may be well given. Within the last twenty years, radical changes have taken place in the methods and appliances for the generation and distribution of power. These changes have been made largely in the prime movers, both as to type and size, and are best ill.u.s.trated by the changes in central station power-plant practice. It is hardly within the scope of this work to treat of power-plant design and the discussion will be limited to a consideration of the boiler end of the power plant.

As stated, the changes have been largely in prime movers, the steam generating equipment having been considered more or less of a standard piece of apparatus whose sole function is the transfer of the heat liberated from the fuel by combustion to the steam stored or circulated in such apparatus. When the fact is considered that the cost of steam generation is roughly from 65 to 80 per cent of the total cost of power production, it may be readily understood that the most fruitful field for improvement exists in the boiler end of the power plant. The efficiency of the plant as a whole will vary with the load it carries and it is in the boiler room where such variation is largest and most subject to control.

The improvements to be secured in the boiler room results are not simply a matter of dictation of operating methods. The securing of perfect combustion, with the accompanying efficiency of heat transfer, while comparatively simple in theory, is difficult to obtain in practical operation. This fact is perhaps best exemplified by the difference between test results and those obtained in daily operation even under the most careful supervision. This difference makes it necessary to establish a standard by which operating results may be judged, a standard not necessarily that which might be possible under test conditions but one which experiment shows can be secured under the very best operating conditions.

The study of the theory of combustion, draft, etc., as already given, will indicate that the question of efficiency is largely a matter of proper relation between fuel, furnace and generator. While the possibility of a substantial saving through added efficiency cannot be overlooked, the boiler design of the future must, even more than in the past, be considered particularly from the aspect of reliability and simplicity. A flexibility of operation is necessary as a guarantee of continuity of service.

In view of the above, before the question of the selection of boilers can be taken up intelligently, it is necessary to consider the subjects of boiler efficiency and boiler capacity, together with their relation to each other.

The criterion by which the efficiency of a boiler plant is to be judged is the cost of the production of a definite amount of steam. Considered in this sense, there must be included in the efficiency of a boiler plant the simplicity of operation, flexibility and reliability of the boiler used. The items of repair and upkeep cost are often high because of the nature of the service. The governing factor in these items is unquestionably the type of boiler selected.

The features entering into the plant efficiency are so numerous that it is impossible to make a statement as to a means of securing the highest efficiency which will apply to all cases. Such efficiency is to be secured by the proper relation of fuel, furnace and boiler heating surface, actual operating conditions, which allow the approaching of the potential efficiencies made possible by the refinement of design, and a systematic supervision of the operation a.s.sisted by a detailed record of performances and conditions. The question of supervision will be taken up later in the chapter on "Operation and Care of Boilers".

The efficiencies that may be expected from the combination of well-designed boilers and furnaces are indicated in Table 59 in which are given a number of tests with various fuels and under widely different operating conditions.

It is to be appreciated that the results obtained as given in this table are practically all under test conditions. The nearness with which practical operating conditions can approach these figures will depend upon the character of the supervision of the boiler room and the intelligence of the operating crew. The size of the plant will ordinarily govern the expense warranted in securing the right sort of supervision.

The bearing that the type of boiler has on the efficiency to be expected can only be realized from a study of the foregoing chapters.