REFRIGERATION EQUIPMENT
AMMONIA MACHINES -- AMMONIA -- COMPRESSOR -- CONDENSER -- RECEIVER --
COOLER -- CONDENSING WATER -- UNIT BASIS -- COMPUTING FROM UNIT BASIS
-- HOW RATED -- FREEZER REQUIREMENTS -- FREEZERS IN SMALL PLANTS --
CYLINDER ARRANGEMENT -- WHY BRINE CIRCULATION -- AIR CIRCULATING
-- FORCE DRAFT -- COIL ROOM SYSTEMS -- BRINE CHILLING -- BRINE
METHODS -- TYPES OF BRINE COOLERS -- BALANCED BRINE SYSTEM -- DIRECT
EXPANSION -- TWO-STAGE COMPRESSORS.
=Mechanical Refrigerating Equipment.=--This agent is of great
consequence in the operation of packing houses, and, therefore, it
is deemed essential to explain the principles briefly; as well as to
describe the uses.
=Ammonia Machines.=--The use of ammonia refrigeration equipment either
absorption or compression has so generally displaced all others for
stationary or land use, and particularly in meat plants and cold
storage houses, that for the present purpose it is unnecessary to
go into a discussion of others. The compression system being so
predominant in its use, a description of same is given.
The diagram indicates a compression system in elementary form
consisting of:
(1) A pump or compressor which withdraws the gas from the cooler or
expansion tank, prepares and passes it to the condenser.
(2) The condenser or liquifier which gives to the water flowing over it
the heat carried to it by the gas from the cooler.
(3) The cooler or expansion tank in which the heat extracted from the
carcasses, the building walls or elsewhere, is passed to the ammonia
gas for conveyance to the condenser.
=Ammonia.=--Leaving for a moment the description of the apparatus to
acquaint the reader with ammonia: In the form used in a compression
refrigerating machine, it bears the name “liquid anhydrous ammonia”
meaning in a “dry liquid” form differentiating from the common
household ammonia which is a water solution containing ammonia gas in
variable quantity. The distinction between these two is that “anhydrous
ammonia” will evaporate to naught; from household ammonia the gas will
evaporate but the water will remain.
[Illustration: FIG. 15.--DIAGRAM SHOWING AMMONIA COMPRESSION SYSTEM.]
Ammonia is a chemical compound made up of one part nitrogen and three
parts hydrogen and is expressed by the chemical symbol NH₃. It has some
peculiar characteristics being analogous to water. It will assume a
solid, liquid and gaseous form, at -115° F. and -28¹⁄₂° F. for solid
and liquid respectively and will modify to a gaseous form at any
temperature above -28¹⁄₂° F. under “atmospheric” or conditions of no
pressure.
Water, as is known, changes from a liquid to a solid at 32° F. and
changes to a vaporous form at 212° F. but here the analogy ceases.
Ammonia has further peculiar advantages for use in refrigerating
production that it becomes a liquid at variable pressures and
temperatures; for example, when the temperature is reduced to 60° F.
under a pressure of 92 pounds, when reduced to 80° under a pressure of
139 pounds and at 100°, under a pressure of 200 pounds; with variables
above, between and below these conditions. Ammonia, as will be seen,
has variable forms and capacities under the conditions imposed upon it.
Substances passing from a liquid to a gaseous form require heat to make
this change and consequently absorb it; the complement to the giving
up of heat when the process is reversed and the substance changed
from a gaseous to a liquid form. The adoption or harnessing of these
principles is the nucleus upon which mechanical refrigerating effect is
built. A pound of water passing to steam will absorb about one thousand
degrees of heat, ammonia has the same characteristic to a different
degree. They both return the heat when the process is reversed.
=Type of Machine Illustrated.=--The diagram illustrates a single acting
pump showing its piston, a liquifier or condenser where the ammonia is
modified in form from a gas as received therein to a liquid; a receiver
to which it flows and a cooler in which it is expanded and where the
heat brought to it by the returning brine is picked up by the ammonia
and carried to the condenser. The arrows indicate the direction of flow.
=Compressor.=--The “Compressor” is a pump, a cylinder fitted with
a piston which withdraws the ammonia from the tank in which it is
expanded. The piston is tightly fitted and when it travels in one
direction, the gas flows in, filling the space, like any ordinary
pump whether it be a water or gas pump. Upon the return stroke, the
gas is compressed in the cylinder until the pressure in the piston is
sufficient to equal or overcome that exerted against it accumulated in
the condenser, when it is discharged thereto. There are spring actuated
valves interposed in the line of gas travel which close and retain in
the condenser that gas which has been discharged, allowing the piston
and compressor to repeat the just described performance many times per
minute.
=Condenser.=--The use of this element is to liquify the ammonia, really
to extract the heat absorbed by the ammonia in the cooler and the heat
generated in the compression. This condensing operation changes the
form of the substance from gaseous to liquid. The most simple style
of condenser is a series of pipes stacked together with ammonia on
the inside of the several pipes, and water flowing over the outside.
The gas on leaving the compressor is hot and at a high temperature,
frequently as high as 250° F. or more, and the pressure from 140 to 220
lbs., depending upon the water supply, its temperature and quantity,
and the area of the surface of the condenser.
The water flowing over the condenser absorbs the heat from within, the
ammonia becoming cooled by contact with the comparatively cool walls
of the pipe while flowing from one end to the other of the condensing
coil, gradually changing from a gaseous to a liquid form.
=Receiver.=--From the condenser the liquid ammonia is collected in the
receiver so as to have a quantity stored for use and in reserve for the
fluctuating requirements.
=Expansion Valve.=--A small but important item in the system is the
expansion valve which is a valve with a controllable opening and
comparatively small. This is interposed in the line between the liquid
receiver and the cooler or expansion tank.
=Cooler or Expansion Tank.=--The next element is the cooler in whatever
form it may exist, whether it be ammonia coils submerged in brine
tank, shell and tube cooler built like a boiler in which the ammonia
surrounds the tube through which the brine solution is pumped, or
ammonia “direct” expansion coils in the air within a room, it matters
not. At this point the heat given off by the substance to be cooled is
absorbed by the ammonia and taken up for discharge to the water flowing
over the condenser.
No substance will change from a liquid to a gaseous form unless heat be
supplied to perform the work of making this change. At the outset it
was stated ammonia will boil or evaporate at 28¹⁄₂° below zero Fahr.
when under no pressure or in the open air. Further, if ammonia be
contained in a vessel and the pressure be reduced below atmosphere,
the boiling point is lowered still further. For example at 10.6 vacuum
gauge pressure the boiling point will be 40° below zero.
Imagine a brine cooler such as a tank with coil submerged and
surrounded by a brine solution: This brine is circulated through
the building and by common knowledge we know it absorbs heat and is
returned warmer than it was sent out. It is supplying the heat for
boiling the ammonia gas.
Reverting to the expansion valves: Assume there is a pressure of 180
pounds in the condenser and a liquid temperature of perhaps 85 to 90
degrees; the same conditions existing in the receiver; also assume
a pressure of 15 pounds on the ammonia coils which will produce a
temperature condition of zero. In the diagram, the coil in the tank
is attached to the expansion valve while on the other end of the coil
is made the connection to the pump or compressor. This by its action
is withdrawing the ammonia gas as rapidly as it is generated, due to
the tightness of the piston, which if it is properly fitted will pump
a vacuum upwards of 22 to 25 inches upon the system attached to it,
unless gas be supplied to fill the space. In operation, the expansion
valve is opened slightly, the liquid is freed into a space where the
pressure is lowered, a condition created for expanding the ammonia to
a gas and the heat contributed by the surrounding brine is absorbed by
the ammonia changing from a liquid to a gaseous form.
=The Cycle.=--The cycle, therefore, is a gas in the expansion tank at
low pressure and temperature, admitted to the pump or compressor under
this condition, compressed to a small volume and increased in pressure,
discharged in this condition to the condenser where it becomes a liquid
and in a condensed form at a lowered temperature and ready to return to
the expansion tank to be used over again.
Ammonia gas is the heat carrier. If it be used in packing house
service, either it absorbs the heat directly from the rooms in which
the animals are suspended or the brine in the tank is circulated
through the rooms to absorb the heat and carry it back to the cooler or
expansion tank.
=Condensing Water.=--In Chapter II reference was made to the condensing
water for refrigerating system. This is important because the lower
its temperature, the less the pressure will be created which means the
less the power must be exerted in the production of the mechanical
refrigerating effect. The water flowing over the condenser carries
the heat to the sewer. Thus the heat from the carcasses, the sun heat
on the walls of the building, the actinic rays through the windows,
the heat from the men employed within, that from the electric lights
within, and that absorbed from the earth upon which the building stands
must all be collected and eventually passed into the sewer.
=Absorption Equipment.=--Absorption refrigeration equipment is used to
some extent in packing house work, but its complexity makes unnecessary
an attempt of its description in this work.
=Unit Basis.=--The unit basis of refrigeration commonly used in
expressing quantity is tons of refrigeration, meaning the tons of
refrigerating duty that can be performed per day of twenty-four hours.
The standard measurement per ton as adopted by the American Society of
Refrigerating Engineers, is a cooling effect equal to 288,000 B.t.u.,
being equivalent to the extraction of this quantity of heat from any
substance.
It has been established by the Bureau of Standards that in freezing one
pound of water at 32° F., to ice at 32° F., 143.5 British thermal units
of heat must be withdrawn from the water. For convenience in practice
the fractional part is ignored, and 144 B.t.u. per pound of water is
accepted as standard in calculations.
=Computing From Unit Basis.=--If 144 B.t.u. are withdrawn from each
pound of water at 32° F. to convert the water into ice at the same
temperature, the melting of the pound of ice at the same temperature
must re-absorb an equal heat in the process of freezing, consequently
the melting of one ton (2,000 pounds) of ice to water at the same
temperature would absorb 2,000 × 144 B.t.u., or 288,000 B.t.u., the
accepted standard for computing the heat absorbed in the performance of
one ton of refrigeration duty. In ice melting this absorption of heat
is _latent_, not sensible to the thermometer, as no change is apparent
by thermometer test in the temperature of the ice and the water,
nevertheless an appreciable _cooling_ of surrounding is measurable
by thermometer wherever ice melting takes place; for example, in an
air-tight room, or in contact with solid substances, or with liquids,
having a higher temperature than 32° F.
=How Rated.=--The rating of refrigerating compressors as usually stated
by manufacturers is expressed in tons. This refers to the tons of duty
that a machine will develop in a period of twenty-four hours continuous
operation under assumed conditions of about fifteen pounds gauge, back
or suction pressure, and 185 pounds head pressure. To perform this
duty the compressor should be of sufficient size to displace or pump
a volume of gas equal to 4¹⁄₄ cubic feet per minute. This rating of
the machine is proper when you are producing temperatures of about
32° F. or over, and presupposes the plant to be properly balanced as
to condensers, and to be properly provided with liquid receivers, oil
extractors and other complementary equipment.
=Freezer-Requirement.=--The growing demand for freezer space in and
about packing houses, however, is so important that special means and
methods must be provided to meet the conditions. It is impossible
to produce freezer temperatures and conditions under the same back
pressure as described above; the back pressures must be lowered and
in doing so the capacity of the compressor is reduced very rapidly.
The same compressor producing one hundred tons refrigeration duty at
fifteen pounds back pressure and 185 pounds head pressure will only
perform half the work when operating under a back pressure of five
pounds, the head pressure remaining the same.
The purchaser must never lose sight of the fact that in cooling freezer
spaces the compressor capacity is reduced practically by half and that
this is applicable to all portions of the system working under these
conditions.
=System to Adopt.=--No hard and fast rule can be adopted regarding
the system of refrigeration to be adopted, whether by use of brine
circulation or direct expansion. The case in hand and the nature of the
business to be done seems to govern. For example, if the plant in which
the business is mixed, wherein hogs, cattle and sheep are killed,
curing performed, and lard made, with a limited amount of freezing,
brine circulation for general use would seem the better. The excellent
results obtained by the use of spray coolers, later described, seem to
point to its use in chilling coolers, with brine circulated through
ceiling or wall coils for cooling storage rooms.
=Freezers in Small Plants.=--If the plant be quite moderate in size
and only sufficient to justify the installation of one compressor the
amount of space required for freezing purposes is thus limited, and if
commercial freezer space is available it is a question as to whether
the operator can afford to deplete his small equipment capacity by
installing freezers.
[Illustration: FIG. 16.--SUCTION CONNECTION FOR DUO-PURPOSE COMPRESSOR.]
=Cylinder Arrangements.=--If the plant be sufficiently large so that
the machine equipment can be afforded in two units then it would be
proper to install freezers. Supposing then that the plant justifies
this arrangement the compressors would be connected to the brine
tank for chilling purposes, and to the closed cooler for circulating
purposes. The gland end of the compressors would be arranged so that
they could be operated independently upon the freezer space at will.
=Why Brine Circulation.=--The chief reason for using brine in the
moderate sized plant is that with a reasonably large brine capacity
there is a reserve cold (so to speak) stored in the brine which will
permit of stopping the compressor, the brine continuing in circulation
by pumping, and there is less likelihood of changes in temperature.
Direct expansion chilling requires an almost constant machine operation.
=Air Circulating.=--The chilling of packing houses and methods involved
are various, each with its advocates. In Europe and where English
methods are followed the system is chiefly forced draft. This system
has been used to some extent in the United States, but the majority of
the coolers are handled with lofts, and circulation therefrom is of
natural sequence. The cellars and freezers are handled by pipes hung in
the rooms.
=Force Draft.=--The force draft or indirect cooling system consists of
forcing chilled air, cooled by passing through batteries of expansion
coils operated dry, or over which brine is passed, through a series
of ducts, and withdrawing it; thence passing it through the coils and
repeating. It is not favored among American packers owing to a belief
that it increases shrinkage, and tends to darken beef; that large
quantities of cold air are lost through open doors; because of the
expense of operating fans, as well as the room taken up by ducts and
the interference occasioned with meat rails.
=Coil Room Systems.=--The overhead bunker system as described under
“_Construction_” in this work details the application of the United
States practice.
Accepting the use of the coil room system and of still storage the
question arises as to the application. A visit of inspection to the
various packing plants throughout America will impress one with the
fact of the existence of a wide variation of opinion and practice with
regard to the methods of applying refrigeration for packing house
purposes. There are two principal applications--direct expansion,
wherein the ammonia gas is circulated through the coils throughout the
premises, and brine circulation, open or closed, where chilled brine is
circulated throughout the works.
=Brine Chilling.=--The two types of brine chilling, open and closed,
produce the same result, except as to the actual brine cooler, of which
there are several, namely:
(1) Brine tank in which are submerged ammonia expansion coils.
(2) Double or triple pipe coolers in which brine and ammonia are
circulated in annular spaces between pipes.
(3) Shell type coolers in which the brine is passed through tubes
within a shell similar to an ordinary flue boiler.
For a close brine system, which is the term applied to a system where
brine is circulated through pipes and not exposed to the atmosphere
so as to absorb moisture, the shell type cooler is a convenient and
economical means of chilling brine. It is so readily applicable to the
use of a balanced system, thereby lessening the power requirement for
pumping.
Double pipe coolers can be used in the same method, but are not quite
so favorably considered owing to the aggregate quantity of joints.
Either the shell type cooler or the double pipe cooler can be safely
used with an open system. The open type brine system is any system used
wherein the cooling effect is produced by bringing the cold brine in
direct contact with the air to be chilled, as in the spray system, the
“Gardner” sheet system, or an open pan system.
=Brine Methods--Recommendation.=--Where it would seem best for other
reasons to use a brine system, and the plant would justify the
expenditure, it would appear well to use a double brine system--open
brine in the hog chill rooms, and a closed system on the freezers, beef
chill rooms, storage rooms.
=Types of Brine Coolers.=--Open tanks with submerged coils are used on
some plants. The investment is greater, but the risk is slightly less
than in the use of closed type brine coolers, commonly called shell and
tube type. Unless the engineering force of the plant is fully qualified
and alert, there is danger of diluted brine and freezing the solution
in shell type coolers, which is likely to split the tubes, causing
leaks and the possibility of brine finding its way to the ammonia
compressors, rendering them liable to damage of a serious nature.
Whereas, with the open type tank and submerged coils, weakened brine
might cause ice to form on the expansion pipes and render them inert,
but no comparable damage could arise. However, we advocate an alert
engineering force and the closed system.
[Illustration: FIG. 17.--DIAGRAM SHOWING BALANCED BRINE SYSTEM.]
=Balanced Brine System.=--The balanced brine system as referred to in
the preceding, is indicated by diagram and has the advantage of keeping
the pipes full at all times, also of reducing the power requirement to
the actual friction through the pipes in the shell type cooler, and a
slight increase for passing through the coils. In practice twenty to
twenty-five pounds friction represents the total head to pump against
in a building nine stories high. The two types of the balanced brine
system are as follows:
_Open System._--Beginning at shell and tube coolers the brine passes
into supply pipes which decrease in size as they approach the ends. The
return line tapers in opposite direction. The pressure carried is only
sufficient to make a sufficiently rapid circulation.
A small pump is inserted in the line so that the pressure can be
increased on that portion through the spray nozzles. This lessens the
power over carrying the entire system at a high pressure.
The balance tank is located at such point as will best serve to collect
the brine from closed coils and the return from the spray coolers. A
vacuum valve is put on the closed line to prevent siphon.
A return connection to the main pumps is made, and also connections to
the concentrator from balance tank so that a portion of the brine can
be concentrated.
This system requires more concentration than the closed system. It has
the advantage that coolers can be used as sharp freezers if insulation
be proper.
_Closed System._--Beginning at shell and tube coolers the discharge
mains and piping are the same as for the open system. Return mains as
indicated. Balance tank is located elevated above upper coils.
A localized defrosting system is installed with individual pump
circulating brine over coils, continuously as required. The collecting
tank is located as near as convenient to lessen pumping head. The brine
flowing over coils in the lofts is concentrated to a strength equal to
circulating brine and introduce into circulation replenishing brine for
defrosting from mains. Concentrator is located where suitable.
In using closed coils the arrangement is different for beef and hogs so
as to assist in the circulation for hog cooler with a view to producing
uniform temperatures.
[Illustration: FIG. 18.--CONCENTRATING ARRANGEMENT, BALANCE BRINE
SYSTEM, CLOSED TYPE.]
In any system using open brine, there is a quite appreciable gain in
the quantity of brine in the system, and a weakening of its strength
lowering the freezing point. This necessitates vigilance as if the
brine weaken too much there is a possibility of it freezing solidly and
insulating submerged coils in an open brine tank rendering them inert
or splitting the pipes in a shell type cooler with disastrous results.
It is consequently necessary to evaporate the brine which can be done
with a concentrator as provided for in Figs. 17 and 18.
The concentrator apparatus consists of a balance or storage tank in
elevated position according to whether the closed or open system is
used; one or more stands of pipe coils; a catch pan for concentrated
brine; a reservoir and a small pump for passing brine into system.
The brine flows from storage tank, entering the bottom pipe of the
coils and passes upward through seventeen pipes, from which point it
is delivered to the trough at the top of the coil and allowed to flow
down over the entire battery of pipes, steam being circulated through
the top six pipes, thus heating the brine and concentrating it by
evaporation. The hot concentrated brine is cooled as it passes over the
lower seventeen pipes through which it originally entered as cold weak
brine.
=Direct Expansion.=--Many plants are equipped completely with direct
expansion systems. This is quite satisfactory provided means are
arranged to dispose of the accumulating ice and snow on the coils.
This is particularly applicable to coils in pipe lofts where moisture
rapidly accumulates, and is accomplished by some arrangement of
defrosting such as circulating a brine over coils by permitting it to
drip over the coils, pumping over and over again.
=Two-Stage Compressors.=--The revising editor brought into prominence
the two-stage compression system by building a successfully operating
plant which functioned with quite astounding results. The system
consists of a large low temperature gas compressor and a smaller second
stage compressor, arranged the reverse to a compound steam engine.
Ammonia gas which at the low temperatures resulting when low
back-pressures are required, becomes highly attenuated (light), it
is necessary to handle a very large volume per ton of refrigeration
developed. To provide for this, the low pressure cylinder is made about
double the volume of the high pressure cylinder.
In the low pressure cylinder the gas is compressed to a pre-determined
pressure and passed at a relatively high pressure, making for a very
high efficiency. The gas is chilled by the introduction of expanded
ammonia to take up the superheat.
The use of this compressor arrangement with its refinement makes an
economical cold producing unit. A record of one year’s run follows:
TWO-STAGE COMPRESSION SYSTEM.
Per Per
year. ton.
Tons received 60,000
Cu. ft. space cooled 2,930,000
Coal cost $17,309.11 .288
Labor 15,156.73 .252
Oil and waste 1,030.82 .017
Water and chemicals 2,103.21 .035
Repairs and changes 1,698.38 .028
---------- ----
Total cost $37,298.25 .62
Expense per cu. ft. space per year .013
=Ample Capacity.=--All of the above factors must be considered in the
calculations for refrigerating requirements, and it is best to make
allowances for a considerable factor of safety over and above the
actual maximum, as well as for the economical operation of the plant.
It never pays to crowd a plant to its limit or capacity. Guard against
emergencies and possible abnormal demand for refrigeration by providing
ample equipment. The plant should be constructed as far as possible in
duplicate, not only as regards the machinery but also in the apparatus,
as a safeguard against accidents and total cessation of refrigeration.
With two machines and duplicate apparatus one-half the maximum
refrigeration is always available, and the preservation of the product
in storage is assured, even if it be found necessary to stop killing
for a sufficient period to make the repairs on the broken machinery or
apparatus, while with one machine only available, a breakdown might
result in a very serious loss and considerable damage to the stored
products.
With regard to insulation, it may be said that the best is the
most economical in the long run. There is no such thing as absolute
insulation, some heat leakage must occur through the very best
insulation, and the reduction of this heat leakage to the minimum
should be the chief object or factor for consideration. First-class
insulation costs more in original investment, but it creates a
continuous saving and economy in refrigeration, resulting oftentimes in
a less investment also in refrigerating, pumping and steam equipment.