Calorimetry system

A calorimetry system for measurement of the heating value of coal having a combustor 24 and a mixing unit 30 wherein heat from combustion gases is transferred to air. The system has a gravimetric feeder 64 for providing coal at a measured mass feed rate; the coal including any moisture present therein. The coal is pulverized in an air-driven mill or pulverizer 14 which is fed coal from the feeder and is separated by a cyclone separator 16 into two streams; one carrying coal and air mixed together in a controlled ratio to the combustor. The air which drives the separator, together with fines of the coal and moisture is fed to an afterburner 26 of the combustor so that the thermal dynamics of the entire coal stream is involved in the heating value measurement. Instrumentation measures the flow rates of cooling air, primary air which carries the coal streams into the combustor and secondary combustion air as well as the mass flow rates of the coal into the combustor as measured with the gravimetric feeder. A computer, thermocouples and pressure gauges controls the feeding of the coal and fuel gases (propane) during initiation of combustion, and for computing the heating value of the coal.

Included as an appendix to this application is the aforesaid patent 
application by Homer et al., which describes a calorimetry system for 
measuring the heats of combustion (heating value) of solid fuels such as 
coal by the continuous combustion thereof, rather than, as in the past, by 
combustion of a discrete sample of the coal as with a bomb calorimeter. 
Techniques of measuring heating value on a continuous basis heretofore 
required reliance on indirect chemical and physical analysis, such as with 
X-ray fluorescence or neutron bombardment (the so-called prompt neutron 
activation analysis technique). Continuous flow combustion calorimetry has 
been used to measure the heat of combustion of gaseous fuel; however the 
accurate continuous combustion calorimetry of solid fuels, particularly 
coal, has not been obtained prior to the invention described in the 
aforementioned patent application. 
This invention has as its principal feature improving the accuracy of 
measurement of the continuous flow calorimetry system described in the 
above identified application and to enable measurements to be made with 
moist coal of low heating value as is commonly used by public utilities in 
the United States. 
Another feature provided by the present invention is to provide an improved 
gravimetric belt feeder capable of measuring the mass feed rate of solid 
fuel, particularly coal, to a high degree of accuracy (for example, less 
than 2% measurement error). 
A still further feature of the invention is to provide an improved 
combustor for coal calorimetry wherein more reliable ignition is 
facilitated by a remote mounted (from the coal combustion chamber) 
ignition device which is immune to the high temperature effects of the 
combustor. There is a high degree of assurance that all parts of the coal 
stream are burnt by using an afterburner which receives fines, together 
with moisture from the coal and air. The air drives a separator for 
producing coal particulates from which a controlled mixture of coal and 
air can be obtained for combustion. The combustor also has improved means 
for clean out of channels through which the mixture of coal and air is 
supplied thereto. 
Another feature of this invention is to provide an improved calorimetry 
system for obtaining the heating value of solid fuels, particularly coal, 
as well as its sulfur content and also its ash content wherein heating 
value, sulfur and ash content can be measured simultaneously and the 
measurements can be made in real time. 
Briefly described, an improved calorimetry system in accordance with the 
invention has a feeder which measures the mass feed rate of coal or other 
solid fuel including the moisture thereon or therein. For optimum 
combustion of the coal, a controlled ratio of air and coal is obtained by 
pulverizing or milling the measured mass of coal, which arrives 
continuously from the feeder, and separating the coal into first and 
second streams, one of which contains substantially all of the coal which 
has been milled to predetermined size and which is mixed with primary air 
in a controlled coal to air ratio. The other stream from the separator may 
contain coal fines and moisture. The exclusion of this second stream from 
the calorimeter would introduce a measurement error of the heating value 
of the coal. The primary coal and air stream, because of its controlled 
mixture, is combusted entirely in the combustor with secondary air which 
passes through a permeable enclosure which serves to minimize heat loss 
from the combustor to the ambient by way of radiative losses through the 
walls of the combustor. The second stream of air, fine coal and moisture 
is introduced into an afterburner wherein all of the coal is exposed to 
the exhaust flame from the combustor so that it may be burned and 
contribute to the heating value measurement without contaminating the 
secondary air which is supplied through the permeable enclosure to the 
combustor. 
In order to initiate combustion and bring the system to a temperature which 
will support spontaneous combustion of the mixture of coal and air, a 
gaseous fuel, preferably propane, is used. This fuel can be used in an 
igniter which introduces a flame into the combustor so as to ignite the 
fuel gas which is initially introduced therein to preheat the system to a 
temperature which enables the spontaneous combustion of the coal and also 
to calibrate the system. Preferably the propane use for calibration 
purposes is substantially pure propane. 
The combustion gases are mixed with cooling air and the heating value is 
determined by a method of mixtures technique. Instrumentation is provided 
for measurement of temperatures and mass flow rates of the air and 
air/fuel mixtures which enter the combustor, and also of the cooling air 
which is used for mixing, so that the enthalpy of all of the constituents 
which affect parameters of the heating value computation is taken into 
account in the heating value computation. A computer is preferably used to 
respond to the measurements from the instrumentation and provide the 
heating value computations which may be printed out and/or displayed. The 
measurements may be used in real time to control processes using the coal, 
such as the rate at which coal is fed to a boiler in a public utility or 
to check the quality of the coal going into storage in a facility, such as 
the coal storage yard of a public utility. 
The combustion gases from the calorimeter may be supplied to a sulfur 
dioxide measurement device for the continuous on-line measurement of the 
sulfur content of the coal stream. The flue gases may also be passed 
through a device which collects the ash, wherein the ash is weighed, so as 
to measure the ash content of the coal. The combustor converts 
substantially all of the fuel into combustion gases without deposition of 
any ash in the combustor. Accordingly the ash measurement device provides 
accurate ash content measurements from the combustion gases. 
The gravimetric feeder is capable of more accurate measurements of the mass 
feed rate of the coal than was the feeder described in the above mentioned 
United States patent application by means for controlling of the length of 
a body of coal. The body of coal is disposed on a lever defined by a 
moving belt onto which the coal is deposited, and which moves continuously 
between a tail and a head end pulley. Means are provided in cooperative 
relationship with the belt as it rotates around the head end pulley for 
providing a defined angle of repose of the end of the body of coal which 
is deposited on the belt and which is fed from the belt into the mill and 
separator of the calorimetry system. Such means is preferably provided by 
utilizing a rotating member which engages the coal adjacent to the head 
end pulley at a velocity at least slightly in excess of the velocity of 
the belt as it travels around the head end pulley. The coal does not 
therefore back up on the belt. The head end pulley is of minimum diameter 
to enable the belt to conform to it and remain in engagement with its 
periphery. The tendency is minimized of the coal to adhere to the pulley 
and thereby to effectively increase the length of the lever arm by 
indeterminate amounts, which can depend upon its cohesivity which is a 
function of several variables, including ambient, environmental 
conditions. The pivotal support for the feeder, which defines the fulcrum 
of the lever, and a force measurement device (e.g., a load cell) are 
preferably made of material having substantially the same coefficient of 
thermal expansion so that the lever arm lengths and the forces which are 
measured by the load cell do not contain errors due to differential 
thermal expansion.

Referring more particularly to FIG. 1 there is shown an input coal supply 
to a feeder 10 which provides a mass feed rate measurement. The output of 
the feeder is a force measurement indicated as WT which is converted into 
a mass feed rate measurement by taking into account the feed rate of the 
coal along a lever arm provided by a belt which extends between tail and 
head end pulleys. This feeder is shown in greater detail in FIGS. 4 
through 7, and will be described fully hereinafter. The computer 12 
provides a control output CF to the feeder which controls the speed 
thereof so as to maintain the feed rate essentially constant. The feeder 
is designed in accordance with features of the invention to provide for 
high accuracy of measurement by assuring that the length of the lever arm, 
which produces a reaction force measured by a load cell to provide the WT 
output, is constant during operation of the feeder. 
The coal is delivered from the feeder to a pulverizer 14. The pulverizer is 
a fluid energy mill in that it is driven by high pressure air (HP air) 
which is the source of pulverizing energy. The coal from the feeder is, 
for example, approximately 30 mesh. The pulverizer 14 reduces the coal to 
micron size. The moisture in the coal remains during the feeding and the 
pulverizing process. 
The coal for combustion is desirably separated from the air which energizes 
the pulverizer. Practical separators, such as the cyclone 16, which is 
used to separate the coal from the air, entrains with the air a small 
quantity of ultrafine coal, for example, approximately 1% or less of the 
pulverized coal. In order to provide high accuracy in the heating value 
measurement, this coal must also be accounted for. The moisture is also 
carried by the air and must be accounted for. To this end two streams are 
obtained from the cyclone 16; an essentially solids discharge stream along 
the line 18 and an essentially gaseous discharge stream along the line 20. 
Both of these streams are supplied to the calorimeter 22. 
The calorimeter includes a combustor 24 which has an afterburner 26. 
Ignition of the gases in the combustor is started by an igniter 28. The 
calorimeter also includes a mixer 30 which mixes the combustion gases with 
cooling air. The air and the combustion gases leave the mixer as flue gas 
along the line 32. The temperature rise of the combined combustion gases 
and cooling air is used together with the mass feed rates of the coal and 
the total air entering the calorimeter 22 to compute the heating value of 
the coal. These temperature measurements are obtained from thermocouples 
and other temperature measurement devices and data representing them are 
applied to the computer 12 together with pressure measurements PV which 
are obtained from flow measurement devices in lines of a calibrated air 
supply 34. In practice, the supply 34 is provided by a blower and an oil 
free 100 psi source, and will be discussed more fully in connection with 
FIG. 2. 
The temperature and pressure of the air determines the density of the air 
which affects the mass flow rate of the air (viz, the enthalpy of the 
system). The air which energizes the pulverizer and carries a controlled 
mixture of air and coal particles of the cyclone 16 is obtained from the 
calibrated air supply 34. The pressure measurements PV which determine the 
flow are shown for simplicity as being taken from the calibrated air 
supply. The temperature measurements shown at Te are taken in the lines 
directly leading into the calorimeter as will be more fully shown in, and 
explained in connection with, FIG. 2. The coal particles from the cyclone 
16 are educed with low pressure air (LP air) from the supply 34 by means 
of a Venturi educer 36. The air containing the moisture and ultrafine 
particles is supplied to the afterburner 26 where the ultrafine coal is 
combusted in the flame from the combustor. 
To start ignition in the combustor, a preheat fuel supply 38 of fuel gas, 
such as propane, is supplied to the igniter together with air from the air 
supply 34. The igniter includes an electrically operated spark source 
which is energized upon command from the computer and de-energized when 
combustion is detected as by a rise in the temperature of the flue gas in 
the line 32. The preheat gas (which can be ordinary commercial grade 
Propane) is also supplied to the combustor during a preheat cycle. 
When the combustor 24 is preheated to a temperature of between 1500.degree. 
F. and 1700.degree. F. as measured by a thermocouple which measures the 
temperature of the combustor, a calibration mode is entered wherein 
essentially pure fuel gas (propane having a heating value which is known 
to a high degree of accuracy) is supplied to the combustor. This 
calibration mode is carried on without the introduction of any coal from 
the feeder, pulverizer and cyclone. 
After calibration a standby mode is entered while the temperature of the 
calorimeter is maintained with the gaseous fuel from the preheat fuel 
supply. In order to analyze coal, an analyze mode is entered. The feeder 
10 is brought up to speed. The weight is monitored so as to obtain data 
that coal is being fed from the feeder into the pulverizer. Now both 
propane from the supply 38 and coal are entering the combustor 24. The 
temperature of the combustor and the flue gas increase indicating that 
coal combustion is taking place. The propane supply 38 is terminated and 
coal combustion continues. The measurements of temperature and pressure 
are supplied to the computer and the heating value of the coal is 
continuously determined in real time. These values can be displayed and 
printed with the display updated and printing occurring at fixed 
intervals, such as 1 minute, 5 minutes 1/2 hour, etc. The computer may 
also average the heating value measurements during each interval. 
The flue gases may also be analyzed, continuously and in real time, for 
sulfur and ash content. FIG. 1 illustrates a sulfur dioxide (SO.sub.2) 
detector 44 and an ash detector 46 in the flue gas stream. The SO.sub.2 
detector may divert a sample of the flue gas to an analyzer, such as an 
ultraviolet spectrometer of the type which is commercially available. The 
SO.sub.2 output SW is supplied to the computer which may control the 
display and print out so as to provide readings averaged over the readout 
intervals. The ash detector 46 may be a electrostatic precipitator which 
has vibrating plates. The ash precipitates on the plates and is 
continuously weighed to provide an analog weight output signal AW which is 
digitized (as was the SO.sub.2 signal) and supplied to the computer for 
computation of the statistics of the measurements of the ash and sulfur 
content. These ash and sulfur signals may be used together with the 
heating value data to control the mixture of the coal with other coals 
which have previously been measured to provide coal of predetermined 
sulfur content. The ash detector is enabled to provide accurate 
measurements of ash content since the combustor in the calorimeter 22 
collects essentially no ash but rather causes the entrainment of all of 
the ash with the combustion gases so that they pass out of the calorimeter 
22 completely with the flue gas. Parallel operating with the SO.sub.2 
analyzer is possible because of the very small quantity of total flue gas 
required for SO.sub.2 analysis. 
Equations (1), (2) and (3) given below are used to compute the heating 
value of the coal in the computer 12. 
##EQU1## 
where, aa, bb, cc, dd, kk: are coefficients--which are the same for each 
rank of coal (e.g., bituminous, subbituminous, lignite, etc.), T.sub.o, 
T.sub.i are heat exchanger outlet and inlet temperatures; ama is heat 
exchanger air mass flow rate plus combustion air cmb; amc is coal mass 
flow rate; ccair is primary air mass flow rate; cpair is pulverizer air 
mass flow rate; T.sub.i c is combustion inlet air temperature; T.sub.i p 
is primary air inlet temperature; T.sub.i a is afterburner air 
temperature; hv equals coal heating value BTU/pound; and cmb is the 
combustion air mass flow rate. 
These designations are shown in FIGS. 1 and 2 at the lines carrying the 
respective air flows and where the respective temperatures are measured. 
In equation (3), the term 410[f(delta T.sub.a m b)]/amc is the nonspecific 
heat loss which is determined empirically based upon the differences 
between the heating value measured with the calibrated propane and the 
known heating value of the calibrated propane. The term includes a factor 
f(deltaT.sub.a m b) which is a function of the difference between the 
ambient temperatures T.sub.amb upper and T.sub.a m b lower as measured by 
a thermocouple outside of the calorimeter (near the wall of the mixer and 
combustor) and the temperature of the mixing air T.sub.i (also referred to 
as cooling air above) as shown in FIG. 2. These temperatures are used 
because the nonspecific heat loss is a function of the ambient 
temperature. The coefficients aa, bb, cc, dd, and kk may be determined in 
a manner similar to that discussed in the above referenced U.S. Pat. 
application Ser. No. 036,048. These values are also obtainable from texts 
on the thermodynamics of coal. Reference may be had to Chemical Engineers 
Handbook fifth edition, published by the McGraw Hill Book Company, 
Copyright 1973 in the section on heat capacity which will be found on 
pages 3-235 through 3-238, or appendix A entitled Property Data Bank in 
the text, The Properties of Gases and Liquids, by Reid et al. (McGraw 
Hill, N.Y. (1977)). These coefficients are equivalent to the WXYZ 
coefficients of the equation identified by (4) in the above referenced 
patent application where the derivation of these coefficients is shown. 
Referring more particularly to FIG. 2, the thirty mesh coal, which may be 
sampled from the coal stream to the boiler for real time control of the 
coal feed to the boiler in accordance with the heating value thereof, is 
fed into a vibratory feeder 60. From the feeder 60 the coal enters a screw 
or auger type feeder 62 from which it is deposited onto the belt of the 
gravimetric, belt feeder 64. Feeder 10 (FIG. 1) is a combination of the 
screw and belt feeders. The belt feeder is shown diagrammatically in FIG. 
2 as having a head end pulley 66 and a tail end pulley 68 which is driven 
by a stepping motor 70. The stepping motor is controlled by a motor 
controller indicated as FC900 to which on-off control signals and speed 
control signals f.sub.s from the computer are fed (see also FIG. 3). The 
frequency of the f.sub.s signals (which may be pulses) determines the 
speed of the motor when it is turned on or off by the on-off control 
signals from the computer via a digital data board 45 (FIG. 3) which 
contains buffers and drive amplifiers. The f.sub.s signals are provided 
directly from the computer 12 (FIG. 3). The control signals to a similar 
motor 71 which drives the screw feeder 66 are also provided from the 
computer 12 and digital data board 45 to the FC-901 controller. 
The feeder defines a lever which is supported on a fulcrum as will be more 
fully explained in connection with FIGS. 4 through 8. The reaction force 
corresponding to the weight of the coal on the belt is measured by a load 
cell, indicated at WE800. The transducer amplifier of the load cell, 
ihdicated at WT801, provides an analog signal corresponding to the force 
developed due to the weight of the coal on the belt. This analog signal is 
provided to one of six metering circuits and a serial converter which is 
connected to an analog data board 47 of the electronic portion of the 
system, shown in FIG. 3 and which will be described hereinafter. 
The mass feed rate of the coal is determined from the force measurement, 
the speed of the motor 70 and other parameters which will be explained 
hereinafter in connection with FIGS. 4 to 8. As will be described in 
connection with FIGS. 4 to 8 a strip of coal of constant thickness ad 
length is measured, since the end of the strip at the head end pulley 66 
is controlled by controlling its angle of repose on the pulley. The 
measurement is used in determining the heating value of the coal in 
accordance with the equations (1) to (3) given above. 
In order to provide micron size coal to the calorimeter 22 so that it will 
be spontaneously combustible and burn completely with essentially no 
collection of ash in the combustor 24 of the calorimeter 22, the coal is 
pulverized by the fluid (air) energy driven micropulverizer 14. The air 
for driving the pulverizer (supplying the fluid energy for pulverization) 
is high pressure air from a compressor which supplies the air at, for 
example, 100 to 150 PSI. The air supply may be calibrated using calibrated 
pressure transducers and meters which are connected during calibration to 
quick disconnect one way fitting; thus providing the calibrated air supply 
34 (FIG. 1). Two of these transducers (CPT) attached to the fittings (QDF) 
and their meters (M) are shown in dash lines at the high and low pressure 
air inputs provided at the high pressure air 100-150 PSI line and the 
blower 91. The air is regulated by a pressure control valve PCV508 with an 
indicator PI508 as shown symbolically in FIG. 2. This valve is also known 
as a regulator valve. It may suitably be set at 100 PSI. 
The presence of an underpressure condition is indicated by a pressure 
switch PS10, which provides an output to the computer 12 for shutting down 
the system in the event of an underpressure condition. The regulated 
pressure is provided by a pilot operated regulator valve PCV78. The pilot 
pressure is obtained by a solenoid operated valve PV505 and a two-way hand 
operated valve H0100. To start the flow of high pressure air for carrying 
the coal to the micropulverizer 14, the solenoid of PV505 is operated with 
a control signal from the computer. This provides pilot pressure to open 
the pilot operated regulator valve PCV78. The temperature of the high 
Pressure air is measured by TE704. Temperature measuring devices may be a 
thermocouple or a Resistance Temperature Detector (hereinafter RTD). The 
flow of this air is measured by a differential pressure transducer PDT104 
which is connected through a pair of hand operated 3-way valves HV604 
across an orifice plate FO304. These valves permit connection to remote 
instruments via 80, 82 and 86 to permit maintenance and calibration of 
PDT104 and PT204. 
High pressure air of known temperature and flow rate (enthalpy) is allowed 
to enter a Venturi feed funnel 84. Valves PV506 and PV507 are operated in 
sequence by the computer, and together with H0403 and FO305 start and 
maintain pulverizer operation. Air flow through the Venturi develops a 
negative pressure in the feed funnel for drawing the coal therein to the 
micropulverizer, wherein multiple collisions of the particles, caused by 
air jets, fracture the coal to a size small enough to ensure complete 
combustion during its brief residence in the calorimeter combustion 
chamber. 
The air carries the pulverized coal from the micropulverizer (the air 
driven mass of coal, amc) to the cyclone separator 16 which separates the 
coal into the primary stream of pulverized coal (amc) and a second stream 
consisting of the air which circulates around the cyclone, the moisture in 
the coal and the small percentage of ultrafine coal which is separated 
with the air from the micron size coal remain in the stream cpair 
delivered by the cyclone. It is this separated air (cpair) which is 
supplied to the afterburner 26 of the combustor 24 of the calorimeter 22, 
as was explained in connection with FIG. 1. 
Returning to the high pressure air, the absolute pressure of that air may 
be measured by a pressure transducer PT204 to supply an absolute pressure 
signal to the computer. The hand operated valve HV609, which may be 
connected to a calibration gauge through the quick disconnect fitting 
attached to HV609, is used to divert the high pressure air to the pressure 
transducer PT204 for absolute pressure measurement. A similar valve HV608 
and pressure transducer PT203 may be used for absolute pressure 
measurement of the air (the ccair) which carries the pulverized micron 
size coal separated in the cyclone 16 to the combustor 24 of the 
calorimeter 22. 
The pressure of the carrier air (ccair) is controlled, suitably reduced to 
10 PSI, by an instrumented pressure control or regulator valve PCV509, 
PI509. The temperature and mass flow rate of the carrier air is obtained 
by an assembly of a thermocouple TE703, an orifice plate F0303 and 
differential pressure transducer PDT103 which is connected across the 
orifice F0303 by hand valves HV603. Thus, the mass flow rate of the air 
and mass flow rate of the coal (amc+ccair) supplied to the combustor is 
continuously monitored and measured. The temperature of the air fed to the 
afterburner (the cpair) is measured by TE710 which provides the 
temperature signal T.sub.i a which was discussed in connection with FIG. 
1. The ambient temperature in the vicinity of the mixer or heat exchanger 
30 of the calorimeter 22 is measured by TE709 which provides an output 
corresponding to T.sub.a m b upper from which the coefficient for 
controlling the offset due to heat losses from the calorimeter can be 
obtained and used in the heating value computation (see equation (3) 
above). 
The secondary, low pressure mixing air is drawn through a filter 89. The 
temperature of this air is measured by TE706 and its relative humidity is 
also measured by a relative humidity detector MT30. The output of TE706 is 
indicated as T.sub.a m b lower and is used with T.sub.a m b upper to 
determine the heat loss if any from the combustor portion of the 
calorimeter 22 (see equation (3)). 
A blower 91 provides the total low pressure air. The blower is turned on 
and off by controlling power to its motor via a motor control FC902 which 
receives control signals from the computer via the digital data board 45 
(FIG. 3). The temperature of the low pressure air from the blower is 
monitored by TE702. The absolute pressure of the low pressure air and its 
flow rate is determined by an assembly consisting of hand valves HV602 and 
HV607, pressure transducer PT202, the calibration of which can be checked 
by a calibrated pressure transducer CPT and gauge which may be connected 
to the quick disconnect fitting QDF. The differential pressure is measured 
by PDT102 across the orifice plate FO302. The low pressure mixing air has 
its temperature measured at a point closer to the mixer 30 of the 
calorimeter 22 by TE705 to assure that the temperature drops in the lines 
to the input of the mixer 30 are accommodated. The mixing or cooling air 
which mixes with the combustion gases is therefore supplied together with 
measurements of its temperature, pressure and flow rate so that the mass 
flow rate of this air may be computed in the computer 12. In other words, 
secondary air to the combustor is measured at FO301. FO302 measures total 
blower air output, which later splits into secondary (combustion) air and 
tertiary (mixer) air. The proportions are adjusted by HO402. Primary air 
(High Pressure Air from the oil free compressor), designated ccair, is 
measured at FO303. 
The combustion or secondary air cmb is supplied through a hand valve HO402. 
The temperature, absolute Pressure and flow rate of the combustion air is 
measured by a similar assembly as used for measuring these parameters of 
the other air components to the calorimeter, namely TE701, a pressure 
transducer PT201 and a pressure transducer PDT101, hand valves HV601 and 
HV606 apply the pressure to these transducers PT201 and PDT101. There are 
also quick disconnect fittings for connection of calibrated pressure 
transducers. 
In order to initiate combustion and perform preheating and also to 
calibrate the calorimeter, two sources of fuel gas, namely preheat fuel 
gas (propane) to initiate combustion and preheat the calorimeter and a 
source of substantially pure propane of measured heating value (calibrated 
propane) are provided. The preheat propane is supplied through two 
solenoid control valves PV501 and PV503 and an assembly of TE700 and 
absolute pressure transducer PT200 and valve HV605 and a flow-rate 
differential pressure measurement device consisting of an orifice plate 
FO300, two coupled hand valves HV600 and a differential pressure 
transducer PDT100, all of which can be calibrated using an accurate 
pressure transducer and meter through quick disconnect fittings. 
This propane is also shunted through another solenoid control valve PV502 
and a hand-operated valve OH0401 to the igniter 28 below the combustor 24. 
Air to the igniter is supplied from the high pressure air source through 
an instrumented pressure control regulator valve PCV510, PI510 and a 
solenoid control valve PV504. A control pulse generated in response to a 
computer signal is applied to a primary of a transformer BY21 or spark 
coil to provide a high voltage pulse to a spark plug BE20 in the igniter. 
On start up of the system, air and preheat propane are provided to the 
igniter while preheat propane is provided to the combustor 24 and the 
igniter is pulsed to ignite a flame in the igniter which ignites the 
preheat propane in the combustor. The igniter 28 is shown in, and will be 
described more fully hereinafter in connection with, FIGS. 8, 10 and 10A. 
The igniter is shut off after ignition by closing the valves PV502 and 
PV504. Preheat propane continues to be supplied through the solenoid 
valves PV501 and PV503 and the hand-operated valve HO400. The temperature, 
flow rate and pressure of this preheat propane is measured with TE700, the 
pressure transducer PT200 and the differential pressure transducer PDT100. 
Preheat propane is continually supplied until the temperature of the 
combustion chamber wall, T.sub.c wall, as measured by TE708 reaches 
operating temperature (which will support ignition of the coal in the 
combustor). The wall temperature of the combustor T.sub.c wall is measured 
by the thermocouple TE708. 
When operating temperature is achieved, the calibrated propane is supplied 
through the valves PV500 and PV503; the preheat propane supply valves 
PV501 and PV502 being closed by deactuation of their solenoids. The mass 
flow rate pressure and temperature of the calibrated propane is monitored 
by PT200, TE700 and PDT100 and the heating value of the calibrated propane 
is measured and compared with its known heating value so that offsets in 
the heating value computation can be obtained. 
The system is then placed in standby mode with the calibrated propane 
supply cut off and the preheat propane resupplied to the combustor. When 
coal is to be analyzed, the screw feeder motor 71 is turned on at high 
speed, as is the belt feeder motor 70. The coal is supplied (amc+ccair) 
with the primary air from the high pressure air source. When operating 
temperature is achieved, the preheat propane is turned off and the heating 
value of the coal is analyzed using the temperature measurements of the 
input mixing air (T.sub.i) from TE705 and the output temperature of the 
combustion gases T.sub.o from TE707. The computer determines the mass feed 
rates of the air supplied to the calorimeter and of the coal and solves 
the equations given above so as to accurately determine the heating value 
of the coal continuously and in real time. 
The sulfur content is determined from the flue gases by an ultraviolet 
spectrometer, the temperature of which is monitored by TE711 and TE712. 
The transducer AY.sub.1 which samples flue gas from the flue of the 
calorimeter 22 provides an output proportional to sulfur dioxide content 
of the flue gas and therefore of the coal. The precipitator and weighing 
means for ash measurement is not shown in FIG. 2. 
Referring to FIG. 3, there is shown the electronic system for the 
calorimetry system shown in FIG. 2. There are the analog data board 47 
with analog-to-digital converters for translating temperature and pressure 
analog signals into digital signals. The meter circuits #1-#6 convert 
other air and propane pressure and temperature signals and load cell force 
signals into digital signals. The microcomputer 12 uses the serial 
converter to read the meters digital signals (into the computer 12) via 
address codes which are carried on the data lines, which lines extend 
through the boards 45 and 47. Multiplexing therefore occurrs. Operation 
control for the system is inputted from a keyboard 43 and outputs to the 
motor controls and the igniter and also to the solenoid valves are 
provided from the digital data board 45 which also contains drive 
amplifiers to provide sufficient current for operating the switches and 
solenoids. It will be understood that there is a separate output from the 
digital data board to each solenoid valve and switch. The speed control 
signals for the motor controllers of the screw feeder FC901 and the belt 
feeder FC900 are supplied as variable frequency clock pulses from the 
computer 12 and alter the speed of the stepper motor 71 of the screw 
feeder 62. The computer operates in accordance with the program, the 
format and structure of which will be apparent from FIG. 11 to execute the 
various modes of operation of the calorimetry system and to compute the 
heating value, sulfur content and other measurements which are made during 
the operation of the system. 
Referring to FIGS. 8, 9, 10 and 10A, there is shown the calorimeter 22. It 
will be noted that in general, the design of the calorimeter 22 is similar 
to the calorimeter shown in the above-referenced United States patent 
application. The improvements in the calorimeter lie in the inclusion of 
the afterburner 26, the manifold piping for distributing the air and coal 
mixture into the combustor 24, which manifold arrangement is shown in FIG. 
9, and in the igniter 28. The mixer, heat exchanger 30 has its center flue 
elongated so that the upper baffle disk 145 is above the heat recovery 
labyrinth 72. 
The coal and air mixture amc and ccair enters the calorimeter 22 by being 
distributed with a manifold ring 76 having three arcuate pipes 78, 80 and 
82 which are connected to a distributor coupling 84. The coupling is 
connected to the eductor 36 via a pipe 88. The manifold pipes are 
individually connected to three discharge pipes 90, 92 and 94. The pipes 
are easily cleaned of any clogs, since their couplings to the manifold 
pipe, the couplings being shown at 96, 98 and 100, can be disconnected and 
rods inserted to clear the pipes, if and when necessary. The ends of the 
discharge pipes are connected through nozzles, one of which 102 is shown 
in FIG. 8, into the top plate of the combustion chamber 106 of the 
combustor 24. There are similar nozzles connecting the two other discharge 
pipes, all of which are disposed at 120.degree. separations from each 
other. 
In the combustion chamber 106, the flow path of the coal is folded back on 
itself and the burning of the coal takes place in the centroid of the 
chamber 106. The circulation of the coal insures that it is fully burned 
without the collection of ash and all ash travels upwardly out of the 
combustor, through the mixer 30 and, finally, out of the calorimeter 22. 
The secondary or combustion air cmb is provided by the blower 91 (FIG. 2). 
The combustion air is suitably 15 SCFM at 20 to 40 inches of water column 
as can be measured by the various pressure gauges and pressure transducers 
in the system. The secondary air gains access to the combustion chamber 
106 by passing through a porous insulator cell 108 of ceramic material 
surrounding the chamber 106. The insulator is heated by radiative and 
conductive loss from the combustion chamber 106 and is cooled by the 
secondary air passing through it. During this passage, the secondary air 
is heated, picking up the radiated and conducted heat loss from the 
chamber 106 before entering the combustion chamber through two sets 110 
and 112 of circumferentially spaced holes. Three additional holes (not 
shown) are disposed from approximately 120.degree. apart in the 
cone-shaped bottom of the chamber 106 to assist in the circulation of the 
secondary air. In addition, there may be air holes spaced behind the 
nozzles 102 which extend downwardly from the distributor tubes 90, 92 and 
94, all to improve the distribution and circulation of the air and coal 
mixture in the combustor chamber 106. The distributor tubes 90, 92 and 94 
also carry the preheat propane and the calibrating propane during the 
preheat, standby and calibrate modes of operation of the system. The rows 
of circumferential holes 110 and 112 are disposed with their axes at 
45.degree. downwardly. 
The igniter 28 consists of a hexagonal cylinder 120 having a combustion 
chamber bored therein. The combustion chamber 122 is sealed at the bottom 
by a plug 124. Tube 126 and another tube 127 approximately 120.degree. 
behind the tube 126 provide inlets for high-pressure regulated air and 
propane into the chamber 122. Also entering the chamber 122 is an ignition 
device, namely a spark plug 128. As shown in FIG. 2, the spark plug BE20 
is connected to the transformer (BY21). A flange 130 is provided for 
connection of the igniter 28 to the housing of the calorimeter 22. A tube 
132 extends from the chamber 122 into the bottom of the combustion chamber 
106. In operation, when a spark occurs in the chamber 122, a flame is 
generated which travels up the tube 132 into the combustion chamber where 
it ignites the propane and air mixture in the chamber to begin the preheat 
mode of operation of the system. 
The afterburner 26 consists of inner and outer cylinders 134 and 136 which 
are closed by a ring 138 at the top of the afterburner. The air for the 
afterburner (cpair) comes from the cyclone. This air carries the moisture 
and the ultrafine coal into the annulus between the cylinders 134 and 136. 
This air circulates and is distributed around the annulus and flows into a 
region between two rings 140 and 142 at the bottom of the afterburner. 
There the coal is exposed to the flame rising upwardly from the combustor 
cell. In other words, the afterburner mixture of coal, moisture and air 
enters radially into the flame, the radial direction being defined by the 
rings 140 and 142 and the annulus between the cylinders 134 and 136. 
Accordingly, complete combustion of the ultrafine coal occurs so as to 
enhance the accuracy of the heating value computation. It is preferable to 
use the afterburner 26 rather than combining the cpair with the secondary 
air (amc+ccair), since the additional high-volume air flow of which the 
cpair consists could extinguish the flame in the combustor. It is also not 
desirable to combine the cpair with the combustion air cmb since the fines 
in the cpair could clog the porous cell 108. 
The hot combustion products and cooling air mix by turbulent flow while 
traveling the length of the mixing and heat exchanger 30. Mixing is 
enhanced by the presence of baffles. These baffles are in the form of an 
alternating series of disks and rings 143 and 144 which increase the 
turbulence of the flow and the mixing. The temperature probe TE707 is 
located at the top of the calorimeter between uppermost disks 145 and 146. 
This disposition of the temperature probe isolates the probe at the 
exhaust outlet from the combustion chamber 106 and its flame to prevent 
temperature measurement errors due to radiant heating of the thermocouple. 
The disks 143, 145 and 146 are connected to a spine 148 which may be 
vibrated to further cause thermal agitation and mixing. 
Heat losses to the mixing chamber are minimized by the labyrinthine pathway 
72 for the cooling or mixing air ama-cmb. Heat passes from the mixture of 
combustion products and cooling air to the metal tubular wall 150 which 
defines the mixing chamber. This heat passage is by convection. Heat also 
passes to the layers of insulation 152 and 154 surrounding the mixing 
chamber. The cooling air flows along the surface of this insulation 
starting at the low temperature end and gains heat as it travels 
downwardly to the entrance openings 156. These entrance openings are 
triangular in shape to increase the turbulence as the cooling air enters 
the mixing chamber. The triangular flaps cut from the wall 150 to provide 
the openings 156 are bent backwardly to provide baffles internally of the 
mixing chamber to facilitate mixing and enhance turbulence. The cooling 
(or mixing) air thus improves the accuracy of the system since it picks up 
radiative, conductive and convective losses from the mixing chamber. The 
heating value computation is carried out using the temperature difference 
between the temperature of the cooling air T.sub.i and the T.sub.o. Of 
course the enthalpy of all of the other materials flowing into the 
calorimeter are taken into account together with the temperature of the 
mixing air T.sub.i in determining the total temperature rise to T.sub.o at 
the outlet of the mixing chamber (the flue) at the top of the mixing 
chamber. 
Referring more particularly to FIGS. 4 through 7 and also to FIG. 7A, the 
gravimetric belt feeder 64 will be shown together with the outlet end of 
the screw feeder 62. 
The belt feeder has as its principal element a belt 200 which is of 
elastomeric material, preferably a fiber reinforced neoprene having a 
width extending between the sides of a support frame 202. The support 
frame has journalled therein a head end pulley 204 and a tail end pulley 
206. These pulleys are shown diagrammatically in FIG. 2 at 66 and 68. It 
is a feature of this invention that the head end pulley is of minimal size 
and is significantly smaller than the tail end pulley which is necessarily 
large to provide the surface area necessary to drive the belt. To this end 
the belt is tightened and tensioned by a tensioning pulley 208. 
One side 203 of the frame 202 extends rearwardly beyond the tail end pulley 
206 and supports a drive motor 210 with its gear reducer 212. A cog belt 
214 connects a motor pulley 216 and a pulley 218 which is connected to the 
tail pulley 206. For balancing and leveling purposes there is a screw 220 
with a weight in the form of nuts 222 which may be adjustably positioned 
on the screw 220 and clamped against each other. The frame is supported as 
a lever on a bracket 224 which is attached to a support structure 226, a 
part of which is indicated in FIGS. 5 and 6. The support bracket is 
approximately the same width as the frame and carries a load cell 228 
which is connected to a mounting plate 230 attached to the support bracket 
by screws 232. The load cell has an actuator button 234 which may be a 
composite of metal and elastomeric material for damping purposes. 
The support bracket has a notch 233 through which the end of the screw 
feeder 62 extends over a guide 238 having side bars 240 and a leveling bar 
242. The coal is deposited into this guide and is shaped by the guide into 
a generally rectangular strip on the top surface of the belt 200. The 
guide is attached to a bracket 241 which is connected to a bar 243 which 
extends across the frame under the button 234. Inside of this bar 243 
there is a blind hole 246 which carries an overload pin 248 against which 
the load cell drive button 234 bears. The overload control is provided by 
a spring 250 which is captured in the hole 246 under the overload pin. The 
spring force developed by the spring 250 is higher than the load cell 
force rating but less than the overload limit of the load cell. 
Accordingly, the load cell is protected by the overload pin 248 and spring 
250. 
The location of the point of contact of the load cell to the overload pin 
is significant in order to provide high accuracy of measurement, since 
measurement accuracy is a function of the direction of the force as 
applied to the load cell. The force component equal to the force due to 
the weight of the coal on the belt (the moment) is directed into the load 
cell without any side forces or loads only when it is along the axis of 
the load cell. Any deviation from parallelism produces side loads on the 
cell which adversely affects its accuracy. 
The fulcrum of the belt and frame assembly is provided by flexures 252 and 
254 which are held against the support structure and frame, respectively, 
by screws 256. It is significant to the accuracy of weight measurement by 
belt feeder 64 that these flexures 252 and 254, which define the fulcrum 
of the lever, be at the vertical center of gravity of the assembly held by 
the frame 202. Since these pivot flexures and the fulcrum which they 
provide is located on or very close to the vertical center of gravity, the 
center of mass is neither above nor below the fulcrum. Therefore, the 
assembly does not exert a moment if it rotates, which might occur due to 
an accidental displacement of the lever or a change in level of the 
support structure 226. This avoids pendulum effects. Also the parts which 
define the fulcrum (i.e. the flexures 252, 254 and the load cell support 
226) are preferably of material having the same coefficient of thermal 
expansion to avoid forces which might produce load cell measurement 
errors. 
In obtaining a horizontal balance, the counterweights 222 are adjusted to 
provide a positive force against the drive button 234, thereby preloading 
the cell 228 and thus avoiding errors from operating tonear the zero load 
condition of the load cell. The point of contact between the pin 248 and 
the drive button 234 is along a radial line to the fulcrum defined by the 
flexures 252 and 254. Accordingly, the axis of the load cell will be 
perpendicular to the radial from the fulcrum and side loads on the load 
cell are avoided, thereby improving its measurement accuracy. 
More specifically, in the feeder there is a first plane which passes 
through the load cell axis and the point of contact of the pin 248 and 
button 234. This first plane is tangent to the radial line (the radius) to 
the fulcrum. The fulcrum is the center of rotation of the assembly. A 
second plane passes through the point of contact and the fulcrum. The 
first and second planes are perpendicular to each other. A horizontal 
plane will pass through the vertical center of gravity and the fulcrum 
which are close to or coincident. 
The load cell measures the reaction due to the weight of the coal on the 
belt 200. This reaction is determined principally by the length of the 
body of coal on the belt 200. This body of coal is shown diagrammatically 
at 260 in FIGS. 7 and 7A. The coal, due to the moisture therein and its 
relatively small particle size, has the tendency to cling to the belt as 
the belt 200 travels around the head pulley 204. This has the tendency to 
form a momntary cantilever of indeterminate length at the end of the body 
of coal. It is an important feature of the invention that the length of 
the body of coal 260 be precisely controlled so that the coal has a fixed 
angle of repose indicated as the angle R.sub.p between a vertical line to 
the center of the head pulley 204 and the leading edge of the coal body 
260. 
This angle of repose is obtained in two ways. First, the head pulley 204 is 
of minimum diameter which reduces the surface on which the coal can bear 
as it slides off the belt. Another contributing element is an angle of 
repose control device or shaper 262 which is disposed above the head 
pulley 204 and has vanes 264 which engage the leading edge of the body of 
coal 260. The shaper is driven at a speed higher than the speed of the 
belt so as to sweep the coal off the belt so that it drops into the feed 
funnel 84 (FIG. 2). Accordingly, the weigh span and resulting moment of 
the coal body is limited and made definite regardless of the cohesiveness 
of the coal. The angle of repose of the coal on the belt at the delivery 
point is controlled and accuracy of weighing is improved. While the vanes 
are shown as fins, they may also be a row of pins and the term "vane" 
shall be deemed to include such pin structures. 
A scraper 266 is mounted opposite to the shaper 262 to clean the belt for 
the next rotation. In order to drive the shaper, a pair of gears may be 
used, the larger gear which is coupled to the shaft of the head pulley is 
shown at 268 in FIG. 4. Its cooperating gear on the shaft of the shaper 
262 is not shown to simplify the illustration. It may be desirable to 
provide a helical twist to the vanes of the shaper 262 to provide a more 
continuous flow of coal off the belt into the feed funnel 84. The vanes 
may be provided by a row of pins which extends radially from the axis of 
the distributor along a helical path from one end of the shaper to the 
other. This arrangement also provides a more uniform flow of the coal and 
provides less surface for adherence of the coal. 
The screw feeder 62 is shown as a tube 63 having an auger made up of a 
helical wire 65 rotatable therein. A separate motor 71 (FIG. 2) is used to 
drive the auger at a variable rate. By reducing the rate of auger feed, 
the width of the body 260 of coal may be adjusted for mass feed rate 
control in the system. 
The computer determines the mass feed rate of the coal from the product of 
the radius of the head pulley and its rpm multiplied by 2 pi/60, so as to 
obtain the rate of movement of the body 260 along the belt in distance 
units per second. This quantity is multiplied by the distance (1.sub.f) 
between the load cell contact point and the fulcrum and also by the force 
detected at the load cell. The entire quantity is divided by the length 
(1.sub.s) of the body of coal on the belt. Expressed mathematically, the 
formula is m =W.sub.r /1.sub.s.sup.2 (ksl.sub.f nr) where m is the mass 
feed rate of the coal, W.sub.r is the force in grams measured by the load 
cell, 1.sub.s is the length of the body 260 of coal on the belt, r is the 
radius of the head pulley, s is the speed of the motor in rpm, and n is 
the ratio of the gears and the pulleys (the speed reduction ratio) between 
the motor and the tail pulley, k is a constant to change the units into 
mass speed rate in terms of grams per second. 
It will be appreciated that the output of the load cell is a current which 
is a function of the weight in grams. This current is converted by the 
analog digital convertor in the meter #6 device (FIG. 3) into a digital 
signal for the computer. Since the motor speed is controlled by the 
f.sub.s control signal, the computer has in its memory the motor speed. 
The other constants are stored in the memory of the computer so that the 
mass speed rate computation can be obtained. The program will be more 
evident from the flow charts in FIG. 11. 
The structure and format of the computer programs which are executed by the 
computer 12 will be apparent from FIG. 11. FIG. 11A shows in general the 
complete program with the program processes for the initialization of the 
system as well as the start-up, calibrate, standby, analyze and shutdown 
modes which were discussed above. 
FIG. llB shows the start-up mode program. It will be noted that the 
computer is executing one of its modes at all times after power up and 
initialization. At the completion of the start-up mode, the calorimeter 
will be at operating temperature and automatically goes into calibration. 
The calibration mode program is shown in FIG. llC. After calibration, the 
system automatically goes into standby. The standby program is illustrated 
in FIG. llD. It will be apparent from the flow chart of FIG. 11D that, 
depending upon operator selection (while the program is waiting for 
operator input from the keyboard), the system stays in standby mode. 
From standby mode the analyze or calibrate mode can be entered. The analyze 
mode program is shown in FIG. 11E. 
From the analyze program the operator can return to standby or shut down 
the system. The shut down program is illustrated in FIG. 11F. After shut 
down the system is prepared to enter the start up mode again when the 
operator selects that mode. 
FIGS. 11G, H and I respectively show the submodules of the start up mode 
program of FIG. 11B. Namely, FIG. 11G shows the blower start up program 
for the low pressure air blower 91 (FIG. 2). FIG. 11H shows the program 
for starting the igniter 28. FIG. 11I shows the preheat Program which is 
used during the start up mode. 
It is desirable to monitor the wall temperature continuously during the 
standby mode thereby protecting the combustor. The program for this 
monitoring operation is shown in FIG. 11J. 
From the foregoing description, it will be apparent that there has been 
provided an improved calorimetry system which is capable of determining, 
to a higher degree of accuracy than heretofore practicable, the heating 
value of coal and other solid fuels in real time and directly, together 
with the sulphur content and, if desired, the ash content of the fuel. 
Variations and modifications of the herein described system, within the 
scope of the invention, will undoubtedly suggest themselves to those 
skilled in the art. Accordingly, the foregoing description should be taken 
as illustrative and not in a limiting sense.