Part 33 (2/2)

In the Ellison fore the lower portion of the ordinary U-tube has been replaced by a tube slightly inclined to the horizontal, as shown in Fig 37 By this arrangeht tube causes a very reater travel of the liquid in the inclined tube, thus per extremely small variation in the intensity of the draft to be read with facility

[Illustration: Fig 37 Ellison Draft Gauge]

The gauge is first leveled byopen to the atmosphere The liquid is then adjusted until its ht-hand leg is then connected to the source of draft byUnder these circuht-hand vertical tube causes the meniscus in the inclined tube to pass from the point 0 to 10 The scale is divided into tenths of an inch, and the sub-divisions are hundredths of an inch

Theoil for the liquid, usually a 300 degrees test refined petroleue is known as the Peabody gauge, and it is shown in Fig 38 This is a ss of the U and with connections such that either a draft suction or a draft pressureacross the tubes are placed at the bottos in hundredths of an inch are obtained by a vernier

[Illustration: Fig 38 Peabody Draft Gauge]

EFFICIENCY AND CAPACITY OF BOILERS

Two of theinto the consideration of what constitutes a satisfactory boiler are its efficiency and capacity The relation of these factors to one another will be considered later under the selection of boilers with reference to the work they are to accomplish The present chapter deals with the efficiency and capacity only with a view toclear exactly what isapparatus, together with thethese factors by tests

Efficiency--The term ”efficiency”, specifically applied to a steaeneration of steam to the total a such generation When this medium is a solid fuel, such as coal, it is impossible to secure the complete combustion of the total ah the grates where it beco unburned, produces no heat Obviously, it is unfair to charge the boiler with the failure to absorb the portion of available heat in the fuel that is wasted in this way On the other hand, the boiler user ainst the combined boiler and furnace Due to this fact, the efficiency of a boiler, as ordinarily stated, is in reality the corate, and

Efficiency of boiler,} Heat absorbed per pound of fuel furnace and grate } = ------------------------------- (31) Heat value per pound of fuel

The efficiency will be the sa its content of moisture For example: If the coal contained 3 per cent of moisture, the efficiency would be

Heat absorbed per pound of dry coal 097 ------------------------------------------ Heat value per pound of dry coal 097

where 097 cancels and the formula becomes (31)

The heat supplied to the boiler is due to the combustible portion of fuel which is actually burned, irrespective of what proportion of the total combustible fired may be[54] This fact has led to the use of a second efficiency basis on combustible and which is called the efficiency of boiler and furnace[55], namely,

Efficiency of boiler and furnace[55]

Heat absorbed per pound of combustible[56]

= -------------------------------------- (32) Heat value per pound of combustible

The efficiency so deter the relative perforrates used under therates could be entirely overcome, the efficiencies obtained by (31) and (32) would obviously be the saaseous fuels, where there is practically no waste, these efficiencies are almost identical

As a matter of fact, it is extremely difficult, if not impossible, to deteruished frorate and furnace This is due to the fact that the losses due to excess air cannot be correctly attributed to either the boiler or the furnace, but only to a combination of the complete apparatus Atte the losses proportionately between the furnace and the boiler, but such attempts are unsatisfactory and it is impossible to determine the efficiency of a boiler apart from that of a furnace in such a way as to make such deterht not lead to endless dispute, were the question to arise in the case of a guaranteed efficiency From the boileran efficiency that has any value when guarantees are to be rate or stoker uarantees as to minimum CO_{2}, maximum CO, and that the aases does not exceed a certain percentage With such a guarantee, the efficiency should be based on the combined furnace and boiler

General practice, however, has established the use of the efficiency based upon co the efficiency of the boiler alone When such an efficiency is used, its exact e, should be realized

The coe is best illustrated by exa data to be deterauge, 200 pounds

Feed teht of coal fired, 17,500 pounds

Percentage of moisture in coal, 3 per cent

Total ash and refuse, 2396 pounds