Calculations in Furnace Technology. Division of Materials Science and Technology

277 Pages·1970·3.775 MB·English

by  Clive Davies, H.M. Finniston, D.W. Hopkins and W.S. Owen (Auth.)

PERGAMON MATERIALS ADVISORY COMMITTEE
DR. H.M. FINNISTON, F.R.S. Chairman
DR. G. ARTHUR
DR. J.E. BURKE
PROFESSOR B. CHALMERS
PROFESSOR A. CHARLESBY
PROFESSOR R.W. DOUGLAS
D.W. HOPKINS
PROFESSOR W.S. OWEN
PROFESSOR G.V. RAYNOR, F.R.S.
PROFESSOR D.W. SAUNDERS
LIEUT-COLONEL S.C. GUILLAN. Executive Member
CALCULATIONS
IN
FURNACE TECHNOLOGY
BY
CLIVE DAVIES
Ph.D. (B'ham), B.Sc. Hons. (Wales), A.I.M., A.M. Inst. F.,
A.R.I.C
Swansea College of Technology
1966
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Copyright © 1970 Clive Davies
First edition 1970
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08 013365 7 (flexicover)
08 013366 5 (hard cover)
To my wife Marion
Preface
THIS is intended as a course book for students taking exami-
nations under the broad subject heading "Furnace Technol-
ogy". It should be particularly useful to students of Metallurgy
taking Furnace Technology at both part II and part IV of the
Institution of Metallurgists examinations. It does, however,
cover the requirements of a large number of professional,
technical and university courses. For this reason, many of the
worked examples have been given in detail. It has been the
author's experience that such a treatment is very necessary
and not an over-simplification.
It is expected that students will be conversant with the ap-
propriate subject-matter of the book, and will have studied, or
will be studying, the more theoretical and practical aspects of
the subject-matter.
xi
Acknowledgements
GRATEFUL acknowledgement is made to the various publishers
and authors who have permitted the use of their illustrations.
Full references are given in the text.
The author also acknowledges the assistance of the Institute
of Fuel, the Institution of Metallurgists, the Institution of Heat-
ing and Ventilating Engineers, the City and Guilds of London
Institute, the Swansea Education Committee, and the Univer-
sity of Wales, in granting permission for the use of past exami-
nation questions. The author accepts full responsibility for any
errors in reproduction of questions and for the solutions given.
Since the change to SI units is imminent a number of the
examples have been changed to what they would probably have
been in this system of units.
Finally, I would like to thank J. N. Harris and D. H. Davies
for helpful suggestions, and D. W. Hopkins, without whose
considerable help and encouragement this book might never
have been completed.
xiii
Introduction
FURNACE technology involves the detailed study of solid, liquid,
gaseous, and nuclear fuels and electric heating as well as the
design of furnaces and other heat utilization devices. In order
to compare the economics of different sources of heat the effi-
ciency of utilization processes must be determined. Furnaces
and boilers using the same or different fuels may be compared
one with another, or with the theoretical thermodynamic heat
requirement for the operation. In order to arrive at efficiencies
of utilization, various calculations have to be made. Thus, the
available heat in fuels (calorific values), the rate of combustion,
and the product of these two, calorific intensity, need to be
determined in order to decide whether sufficient heat of the
required level of intensity is theoretically available in the fuel
to carry out the specified duty.
In evaluating efficiencies, it is necessary to measure the quan-
tity of fuel used, of air entering, and of flue gases leaving the
plant, and the heat lost to the surroundings. In addition, the
effect of insulation upon furnace structures must be calculated
before it is actually installed. For example, in the open-hearth
steel furnace, while heat conservation by roof insulation ap-
pears desirable, any attempt to do so would raise the temperature
of the "cold end" to such a value that the refractory would fail
by deformation under the existing compression stresses. In all
instances of furnace insulation there is an optimum beyond
which the additional cost of lagging exceeds the value of the
heat saved.
When the design of furnaces is under consideration, it is
necessary to calculate the size of flues, combustion space, and
chimneys, and the rating of fans required to supply sufficient
air for combustion. It is also necessary to calculate the pressure
XV
XVI INTRODUCTION
losses that occur throughout the system. Temperatures and
temperature differences must also be known as the basis for
choice of materials and for installation of heat recovery de-
vices.
CHAPTER 1
Introductory
1.1. INTRODUCTION
The fossil fuels—coal, oil, and gas—are at present the most
important sources of energy, although atomic energy is likely
to assume increasing importance. Atomic energy has to be con-
verted into a usable form, generally electricity, and this, at
present, involves normal modes of heat transference.
The instrinsic value of any fuel as a source of heat is related
to the heat which would be produced by combustion under iso-
thermal and ideal gas conditions.
Coal and oil are defined by the geologist as sedimentary
rocks but they differ from all other sedimentary rocks by being
organic (chemical) and it is the release of the heat of combus-
tion of the organic material that provides us with a source of
energy. In most coalfields there is a geological continuity from
peat through brown coals to the anthracites. This change in
rank can be measured by a number of parameters, perhaps the
best function being the increase in carbon content of the vitrain
macιrai, vitrain being one of the four banded constituents that
can be observed by macroscopic examination of coals. Just as
rocks contain minerals, so coals contain macιrais.
No chemical formula can be applied to coal or oil; the for-
mer is a complex organic molecule whose structure has not yet
been elucidated, while oil is a complex mixture of many differ-
ent organic molecules. However, both can be assigned elemen-
tal formulae which indicate the percentages of carbon, hydro-
gen, oxygen, nitrogen, sulphur, and other elements, and this in-
formation is generally sufficient to assess the value of the pro-
D : CIFT 2 1
2 CALCULATIONS IN FURNACE TECHNOLOGY
duct as a fuel. In both cases it is necessary to consider the effect
of any mineral matter which is present, before any calculations
on the basis of elemental composition can be made, since in
many cases the mineral matter can either interfere with the
mechanical processes of combustion or have deleterious effects
on the structure of the combustion chamber.
1.2. PRESENTATION OF ANALYSIS
Solid fuels contain inorganic matter and are usually burned
containing moisture, and the combustion engineer requires to
know the composition and characteristics of the material being
burned—the "as-fired" analysis. Sampling and analysis of fuels
at this stage is generally inconvenient and expensive and it is
necessary to devise a method of presentation which will enable
allowances to be made for variations resulting from changes in
sources of supply and from consequences of storage in the
open.
Analysis may be carried out on "air-dried" fuel, i.e. fuel in
approximate equilibrium with the atmosphere at the prevailing
temperature and humidity, or on the "dry basis", i.e. after
heating to 105°C for at least one hour in vacuo, or in an atmos-
phere of nitrogen. Solid fuel for industrial purposes is purchased
against specified values for heating capacity, moisture and ash
content, chemical composition in respect of certain elements,
and physical condition relative to size. The mineral matter in
coal as mined is not identical with the ash content as determined
by combustion under standard conditions. But there is a com-
paratively simple relationship : the King-Maries-Crossley for-
mula (KMC) where mineral matter (MM) is given by :
MM =1-13 ash +0-5 pyritic S + 08C0 —2-8 S
2
in ash + 2-8SO +0-5Cl.
4
Alternatively, the British Coal Utilization Research Associa-
tion (BCURA) formula, which requires less data, may be used :
MM = 1· 10 ash+0-53 total S + 0-74 C0 - 0-32.
2