UNSEEN LOSS THAT EVERYONE IS SUFFERING
WITHOUT KNOWING IT.
We have so many ways to save energy and most of us seem to look into any method
which gives saving clearly visible to the eye of the management such as waste
heat recovery, change of fuel to lower the cost per Kcal. All these methods
can give a clear figures to the management as to how much money company can
save by calculating value of the heat. However, to the author's knowledge,
most of the steam users do not know that they are losing so much money every
seconds when their boilers operate with fluctuating pressure. People tend to
believe that any heat input can produce energy in a form of steam with a certain
consideration of heat loss which reflects in the boiler efficiency regardless
of fluctuating steam pressure. They say that even pressure changes, we are
getting steam equivalent to what we spend in energy input. This is totally
wrong concept. There are hidden losses of energy or unseen losses of great
amount of money when your boilers are operating with fluctuating pressure.
Every time when pressure drops, you are loosing money. Everytime when the boiler
must rise its pressure to what you need, again, you are losing money. In this
documents, I am going to elaborate why this happens and how we can prevent
it.
LET US KNOW THE FUNDAMENTAL OF STEAM
MOLECULES
Now, we have to go deeper into the characteristic of Molecules of Water. The
molecule in liquid is constant motion, and their speed of movement is dependent
on the temperature. The hotter the liquid the faster do the molecules move.
Owing to the congestion and to their erratic movement collision often take
place. As a result of multiple collision some molecules go, for a short time,
much faster then their fellows who may have been slowed, or even stopped, as
a result of the collision. The more heat we add to the liquid the faster go
the molecules, the more molecules can escape. At the water level of the atmospheric
pressure, molecules of the air-born water and molecules of the water are having
battles all the times. A hail of air or vapor molecules is raining down on
because it always carries some moisture, so that, although some water molecules
are jumping from the water surface some air-born water molecules are diving
back into the liquid.
HEAT IS ENERGY
Heat is a just a form of energy. When heat is added to a substance it is stored
in the substance as extra molecular movement. It's a mechanical movement
and mechanical energy. The greater the weight to be moved, the greater the
energy needed.
WHAT PRESSURE IS
The pressure exerted by a gas or vapor is due to the myriads of impacts of
the molecules bombarding the surface enclosing the vapour. If we add heat
to a gas or vapour in a vessel we increase the speed of the molecules and
therefore the temperature rises. The faster movement of molecules demands
more room, so the vapour tends to expand. If we prevent expansion by keeping
the vessel closed the faster moving molecules , having the same density as
before, must produce a heavier bombardment effect which shows as an increase
of pressure.
VAPOUR PRESSURE
If the pressure on the surface of a liquid
is caused by the rain of air or vapour molecules, it follows
that those molecules trying to jump out of the liquid must
be exerting a pressure on the air or vapour above the liquid.
The pressure at which the escape of molecules from the liquid just balances
the overlying pressure is called the 'VAPOUR PRESSURE OF THE LIQUID".
BOILING POINT
As more heat added to the water, temperature
rises, and more molecules try to jump out of the liquid. Most
of the adventurous water molecules get knocked back into the
liquid, so that practically whole of the added heat energy
is retained as increased molecule speed in the liquid. As the
addition of heat proceeds we reach a point where the upward
bombardment by jumping molecules overcomes the downward bombardment
of the overlying air or vapour molecules. That is to say, the
liquid vapour pressure overcomes the overlaying pressure. The
speeding water molecules, having won the battle, can now leave
the water freely provided they receive sufficient and continuous
energy to enable them to overcome the overlying pressure. At
this point, it is impossible to raise the temperature of the
water, because this would increase the vapour pressure which
can rise as it has already overcome the overlaying pressure.
The particular temperature at which this state occurs is called
as "BOILING POINT".
YOU LOSS MONEY FOR EVERY PRESSURE
DROP
By knowing the characteristic of steam and
its molecules, let us now discuss here how to prevent great
energy loss due to the pressure fluctuation. There are three
cases. Constant pressure, pressure drop and pressure rise.
CONSTANT PRESSURE
When the boiler is operating at the constant pressure, that means the vapour
pressure of the water is equalized with the overlying pressure of the surface
maintaining the Vapour pressure of the water and the boiling point. As long
as these two factor do not change, any heat added to the vessel will let
the escaping molecules to go and that is the evaporation made under perfect
efficiency because all heat input will be transferred to the steam.
PRESSURE DROP
When the boiler pressure drops, it means
overlying pressure on the water surface will decrease. Then
the liquid molecules suffer less interference and can escape
more easily. The water can exert the necessary vapour pressure
at a lower temperature. So, the boiling point of a liquid falls
with reduced pressure. Instantly, water then will be forced
to release energy to the vapour area by allowing molecules
to escape. This release energy is in equivalent to the difference
of sensible heat of the initial pressure and sensible heat
of the lowered pressure. This release is done instantly that
the whole water surface area will be used for maximum vaporization
with the rate of vaporization (Kg/m2 of steam) at the given
pressure. Therefore, this energy is from the energy contained
in water and NOT FROM THE ADDED HEAT. Immediately after the
overlying pressure is equalized with the vapour pressure, no
more molecules can escape without the help of the ADDED HEAT
in order to overcome the overlying pressure. Then from this
stage, as long as the overlying pressure does not change, all
ADDED HEAT will be fully used for vaporization. During the
period of equalization of 2 pressure, steam being released
from the boiler is from the stored sensible heat of the water.
( we call this "DISCHARGING TIME)
And factory will not be receiving any benefit or result from the continuous
firing of fuel, which means A GREAT LOSS OF ENERGY for every pressure drop.
PRESSURE RISE
When pressure rises, overlying pressure on the water surface will become stronger
than vapour pressure. Escaping molecules will meet bombarding pressure above
which prevent molecules to fly off the line. During this period, evaporation
of steam stop. Then water will receive energy from ADDED HEAT to increase
its sensible heat in order to increase its pressure equivalent to the overlying
pressure and increase boiling point. As soon as two pressure equalize, evaporation
will start again . During this period of receiving energy without evaporation
( we call it as CHARGING TIME), all energy from ADDED HEAT is used for increasing
water sensible heat without evaporation. Remember what you need is HEAT FROM
STEAM and not SENSIBLE HEAT. Factory never receive any benefit out of sensible
heat since it is inside the water. Only the LATENT HEAT is to be carried
by STEAM. You are losing money every time when this happens without knowing
it. If there is anyone who argues that the additional heat during this charging
period is used to raise up the pressure even without evaporation so it is
not wasted, to whom I shall say that he might be right if he is needing such
a raise of pressure at that time. However, if such a pressure rise is not
needed, then added heat without evaporation is a total loss to him as the
pressure must be reduced to what he needs immediately after the rise causing
another loss due to the pressure drop as explained herein. |

CALCULATION OF LOSS DUE TO PRESSURE
DROP
Example If we take a small shell boiler
of 4 ton/H capacity, the water content is probably about 7
M3 and the steam content is about 3 M3 in the shell. Let us
consider such a boiler working at 9 Kg/cm2 pressure and let
us see what happens when the pressure is allowed to drop to
8 Kg/cm2 and to rise 10 Kg/cm2. Fig.-1 If the water occupies
7 M3, it will weigh 7 m3/ 0.001118 = 6,261 Kg at 9 Kg/cm2 pressure.
CASE OF 1 KG PRESSURE DROP A deduction in pressure of 1 Kg/cm2
will reduce the sensible heat by; 181.2 - 176.4 = 4.8 Kcal/Kg
This will cause a flash of ( 4.8 x 6,261 ) / 485.6 = 61.89
Kg of steam
(a) We assumed that the
steam space has a volume of 3 M3. Weight of steam in the
steam space at 9 Kg/cm 15.14 Kg Weight of steam in the steam
space at 8 Kg/cm2 13.70 Kg Steam available due to expansion.............................
1.44 Kg of steam
(b) ***So we see that
by allowing the pressure drop by 1 Kg/cm2, we get (a) + (b)
= 63.33 Kg of extra steam from a boiler which is probably
producing 3600 Kg/H(90% load) or 60 Kg of steam/H. This extra
steam represents almost 1 minutes' steaming. CASE OF 1 KG
PRESSURE RISE A rise in pressure of 1 Kg from 9 Kg/cm2 -
10Kg/cm2 will make a boiler absorb 57.6 Kg of steam or equivalent
to 50 seconds' steaming.(Follow the same formula to calculate.)
A pressure variation of 1 Kg/cm2 , if such a variation can
be tolerated, will allow a boiler to carry a 200 per cent.
load for 1 minute to meet a peak demand, or zero output for
nearly 1 minute to meet a valley. From the example just given here, we
see that the steam volume has a very poor storage value compared
with the water volume. In dropping from 9 Kg/cm2 to 8 Kg/cm2
the water provides 61.89 Kg of steam whereas the steam space
only provides only 1.44 Kg of steam. In other words, 8.84
Kg /M3 of steam from the water space, but we only get 0.48
Kg/M3 of steam from the steam space. Volume for volume water
provides 16 times the steam storage as does steam space at
the particular pressure considered. HOW TO PREVENT LOSS DUE
TO PRESSURE DROP Main problem is the continuing fire during
DISCHARGING TIME when ADDED HEAT is not needed. In this case,
the answer is to install another Pressure Vessel without
HEATING SYSTEM ( Unfired Vessel) to take care of CHARGING
and DISCHARGING energy without receiving any ADDED HEAT.
This unfired vessel is the ACCUMULATOR. You want processing
steam pressure to be as stable as possible, but you can not
expect the processing steam flow rate to be constant as the
processing steam demand will always fluctuates. You also
want the boiler pressure to be as stable as possible with
the constant steam flow rate. Then the accumulator will act
as a "CUSHION" between the steam
boiler and process load to absorb all fluctuation of pressure and to react
to the peak load and valley of the processing steam demand without firing.
MORE ABOUT ACCUMULATOR Accumulator can store the steam in a form of water.
Storing steam in a form of steam need so huge space and not practical. Steam
energy from the boiler will come into the accumulator filled with water of
90% of the vessel's space and energy will be stored in a form of sensible heat
in the water and maintain the water in a status of boiling point-( CHARGING
by SENSIBLE HEAT). When the process steam demand calls, saturated water will
instantly release the energy in a form of Latent Heat. Very important thing
to remember is that, as long as steam for heating and processing is concerned,
we are using only Latent Heat and Sensible Heat in the boiler water or in the
condensate is of NO USE.
GREAT ADVANTAGES OF ACCUMULATOR
(1) PREVENT WASTE
YOU ARE NOW LOSING AND MAKE IT AS GAIN. TURN YOUR LOSS TO GAIN
2) BOILER
EFFICIENCY WILL INCREASE AT LEAST BY 5% MAXIMIZE THE EFFICIENCY
GIVEN BY THE BOILER MAKER
(3) CONSTANT PROCESS STEAM
PRESSURE IMPROVES QUALITY OF YOUR PRODUCTS. LEVEL UP QUALITY
AND PROCESS EFFICIENCY.
(4) OPERATE YOUR BOILER
BELOW THE PEAK LOAD FLOW RATE. LOWER INVESTMENT FOR THE RIGHT
CAPACITY OF BOILER
(5) YOU HAVE ALWAYS RESERVED
STEAM FOR USE DURING HOLIDAYS. STEAM REMAINS USEFUL FOR 8
DAYS WITHOUT CHARGING.
(6) RESERVED STEAM IS
VERY HELPFUL FOR EASY START-UP
(7) DRYNESS OF STEAM
INCREASES BY ACCUMULATOR
(8) WHEN USED FOR STEAM
AIR-CONDITIONING, SO GREAT THE SAVING. MANY PART-LOADED BOILER
vs. FEW FULLY LOADED.
From the point of view
of storage, to meet fluctuating load, the bigger the boiler
capacity the better. From the combustion point of view, to
meet fluctuating load, the more lightly loaded the boilers,
that is to say the more boilers there are on the range, the
better, because a given load increase represents a smaller
percentage capacity increase on many boilers than when shared
by few. There are, however, many engineers whose object is
to work as few boilers as possible in order to reduce the
radiation losses. They hold the view that if three boilers
can do the work of four, one quarter of the radiation losses
will be saved. This, of course, is undeniable. However, it
must be noted that any small saving by reducing the number
of boilers on the range is far outweighed by the decreased
efficiency that is given by a boiler on full load compared
to a boiler working on 2/3 to 3/4 load. This gained boiler
efficiency may sometimes amount to 4-5% and saving gained
from which can easily justify the additional investment on
the boiler. APPLICATIONS AND DESIGN CALCULATION OF OF ACCUMULATOR
BASIC DESIGN OF STEAM ACCUMULATOR The accumulator is shown
inFIG.-2. It consists of
a large steel cylindrical vessel nine-tenths filled with
water. It is preferably arranged horizontally so as to give
the largest possible surface of water for the liberation,
as flash, of the stored steam. One pipe A comes to the accumulator
and steam either enters or leaves the accumulator through
this one pipe. When the output of steam and the consumption
of steam are equal there is of course no flow into or out
of the accumulator. It would be silly to discharge and to
charge the accumulator simultaneously; so that one pipe is
all that is necessary. The control of the accumulator is
done by the two valves B and C whose action will be described
later. When steam is passed into the accumulator by the control
valve B it must pass through the charging pipe D because
the non-return valve E closes against it. The ingoing steam
opens the charging non-return valve F and enters the charging
manifold G to which are attached a number of nozzles well
submerged in the water. The nozzles H, although projecting
downwards, blow upwards inside the convection pipes K.
FIG-3 shows an enlarged
section of nozzle. The nozzle encourage rapid circulation,
ensure quick mixing of the water in the accumulator and make
certain that the steam will condensate quickly and quietly
without rattles and bangs. During charging the pressure rises
in the accumulator, the water boiling point rises and so
allows more steam to condense and more heat to be stored.
When the control valve C calls for a steam discharge from
the accumulator pressure in the pipe A falls below the pressure
in the body of the vessel. Non-return valve F closes
which prevents water being discharged, and non-return valve
E opens and allow steam to escape. The lowered pressure in
the accumulator causes the surplus heat in the water to be
given up as flash The nozzle L is a restriction on the flow
of steam which prevents the steam discharging at a dangerously
fast rate which might cause priming or carry-over. STORAGE
CAPACITY OF ACCUMULATOR The amount of steam that hot water
can give up as flash has been discussed already. The water
in an accumulator that is at work is always at the boiling
temperature appropriate to the pressure in the vessel. This
must be so, as were the water below boiling point the steam
above it would condense until the vapour pressures had
equalized; were it hotter the surplus heat would cause a
flash until the vapour pressures had similarly equalized.
The capacity of an accumulator for a given pressure drop
is much greater at low pressures than at high pressures.
A few examples will confirm this. We will take a series of
2 Kg/cm2 pressure drops and work out the effects. Sensible
Heat and Latent Heat at certain gauge pressure are indicated
below; Let us see how much saturated steam at 2 Kg/cm2 gauge
pressure can be stored in 1000 Kg of water at 100 °C . Let
X = (Kg of steam to be stored) (1000 x 99.12) + (X x 650.30)
= (1000 + X) 133.40 99120 + 650.30X = 133400 + 133.40X 650.30X
- 133.40X = 133400 - 99120 516.9X = 34280 X = 66.32 Kg
When the pressure is reduced to 0 Kg/cm2 the surplus heat
available for flash is the difference of Sensible Heat between
the two different pressure; 133.40 - 99.12 = 34.28 Kcal/Kg
And total steam flash will be; (1000 + 66.32) x 34.28 539.40
= 67.77 Kg of steam at 0 Kg/cm2 Working out the other pressure
intervals and starting with 1000 Kg of water, we get as follows;
CHARGE / DISCHARGE CAPACITY OF STEAM PER 1000 KG WATER At
certain pressure ranges
Fig.-(5) It will be seen
that we can take out rather more steam than we put in. This
is because the total heat in saturated steam at one pressure
is more than the total heat in the same weight of steam at
a lower pressure. However, radiation loss from the accumulator,
though very small tends to cancel this because the heat loss
results in condensation, and for practical purposes we can
take output from an accumulator as being the same in weight
as input. RATE OF DISCHARGE FROM ACCUMULATOR The rate at
which an accumulator can be allowed to discharge is limited
by the rate at which ebulition can take place at the liquid
surface without the entrainment of water droplets. FIG.-(5)
shows the maximum rate of discharge recommended based on
our wide experience. Fig.-(7) tell us that if the accumulator
is 90 % full, the water will stand 84% up the vessel and
water surface will be 73% of the surface at the diameter.
We can use this Table to calculate the surface of water inside
the vessel which is very important to know the speed of evaporation
as the quantity of steam per hour that can be released
per SQ. Meter of water surface is fixed at the certain pressure.
` From Fig.-(6), (7) and (8), we can now design the best
suitable accumulator from the available data of the customers
present boiler and processing steam. BOILER FIRING GAUGE
Attached to the accumulator is a pressure pipe leading to
a special pressure gauge fitted in some prominent position
on the boiler firing floor. The essence of the accumulator
is that it permits the boilers to operate at continuous load. This continuous
load should be the average load. But the average load will vary not only from
day to day but to some extent through the day. There must be some method of
informing the boiler house whether the average load is being met. This special
pressure gauge delivers this message. We will assume that the accumulator is
arranged to work over the whole range between boiler pressure and process pressure.
While the boiler operates at constant rating, pressure in the accumulator will
vary between the boiler pressure and process pressure. No precaution may be
necessary to be taken to adjust the boiler firing rate as long as the pressure
gauge indicates within the "CONSTANT FIRING RANGE" preset according to the
condition of the factory. But, if the gauge persistently gives an "Increase" message,
the firing rate of the boiler must be adjusted. Similarly a persistent call
to reduce the firing rate will be obeyed and a drop in accumulator pressure
will be "ignored" until the gauge persistently urges for more steam again.
By means of this gauge, we will be able to adjust the average rate of firing
to suit the true temporary average demand and the accumulator is enabled to
perform its full function of levelling out the peaks and valleys. ART.-( 7)
LOSS OF HEAT FROM ACCUMULATOR An accumulator is usually very lagged with 100-125
mm thickness of first class lagging. It then loses heat very slowly.
Fig-(10)
shows the loss of heat shown by a test taken on the
accumulator over a period of eight days during which no steam
was taken from or put into the accumulator. It shows that
the heat loss was such that the pressure dropped by 0.7 Kg/cm2
per day. The heat loss amounts to the remarkably low
figure of 8.058 Kcal/M2/°C /Hour. Normally, of course, the
accumulator is only intended to store steam for a few hours
at most, but Fig.-(10) shows how useful it can be over extended
periods. In a sugar refinery, for instance, at the shut-down
on Saturday the power load persists for several hours longer
than the process steam load. It is very convenient to be
able to store the resulting exhaust steam that would otherwise
have to be wasted. After a few weeks practice the boiler
house staff are able to arrange things so that the accumulator
is empty just before the shut-down of processing equipments
while the power unit still operating so that the accumulator
can store the exhaust steam efficiently before power unit
shut off. Steam is then available over the week-end for the
canteen, etc.,and for helping to warm up the processing equipments
at the start of operation on Monday morning while the initial
start-up of the boiler unit. GREAT ADVANTAGES OF ACCUMULATOR
FAST RESPONSE TO THE PEAK LOAD WITHOUT CAUSING PRESSURE DROP
Accumulator can store enough quantity of steam just like
a electric chargeable battery and will release necessary
steam quickly responding to the peak load without increasing
the firing rate of the boiler. This is to prevent pressure
drop caused by the peak load while boiler unit usually can
not respond in a short time. Example-1 is taken from one
of our client, a textile mill, whose process steam flow rate
fluctuates between 1.2 to 2.6 ton/h. During 16 hours
operation( 2 shifts), there are only 2 times staring at 6:00am
and another at 1:30 pm when process need peak load of 2.6
ton/h for the span of one hour. After one hour of peak load,
flow rate will go back to normal rating of between 1.2-1.5
ton/h. For this client, we suggested to have 2 ton boiler
to operate constant flow rate at 1.6 ton/h instead of buying
3 ton boiler to meet the peak load of 2.6 ton/h to lower
the investment on the boiler and at the same time to prevent
operating the 3 ton boiler at too low rating( below the economical
rating which is about 60-70% of the boiler capacity). Then
an accumulator was designed to charge the excess steam during
5 hours and to discharge when demand calls during 1 hour
of peak load that happens 2 times everyday during 2 shifts.
With this set up, the boiler of 2 ton/h is operating constantly
at 1.6 ton/h rating to maximize its efficiency for fuel saving
and at the time of peak load, processing steam pressure never
drop down as accumulator can so efficiently discharge the
steam through the main of the pipe line while the boiler
does not need to increase its firing rate. EXAMPLE-II is
the case of one paper mill operating 24 hours a day. 3 oil
fired shell boilers of 5 ton/h capacity are all operating
with common header at the pressure of 5 Kg/cm2. The
process steam demand fluctuates as illustrated in the above
steam flow graph. There are two big valley at 6:00 am and
12:00 noon when changing shift in the morning and lunch time.
The rest of the day, steam flow moves between 7.5 ton/h and
maximum of 12 ton/h. We supplied an accumulator of 65 M3
capacity capable of receiving charging steam from
every valley of (a) to (h) and quickly responding to the demand by discharging
steam for every peak load of (1) to (7). Charging and discharging will be done
fully automatically by the motor or pneumatic valves reacting to the steam
pressure in the steam main to the process line. Any changes of the process
steam pressure above or below the preset pressure of 4 Kg/cm2 will instantly
send signals to the motor or pneumatic valves to react ( as explained with
illustration in Fig.-2). Thus maintaining the processing steam pressure at
4 Kg/cm2 at all time. The boiler will operate at the constant pressure of 12
Kg/cm2 with constant flow rate of 9 ton per hour for 24 hours a day( Instead
of 3 boilers previously operating parallel inefficiently without accumulator,
now one boiler can rest and 2 boilers of 5 ton/h capacity will operate at 85%
load to produce constant steam of 9 ton/h) DESIGN CALCULATION Hereunder is
the desoign calculation to manufacture the best suited accumulator for this
factory. (Case of EXAMPLE -II) (1) Charging capacity of accumulator. From Fig.-7,
we know that accumulator is 90% filled with water standing 84% up the vessel
and water surface is 73 % of the surface of the diameter. We assume; P1: Boiler
Pressure 12 Kg/cm2 P2: Pressure inside the accumulator 4 - 12 Kg/cm2 P3: Pressure
of the process main 4 Kg/cm2 Now, we look into the table below to see how many
Kg of steam can be discharged from M3 of water inside the accumulator under
certain condition of pressure drop P1 - P3. For the case of EXAMPLE-II, we
are given a figure of 69 Kg of steam to be discharged per M3 of water at P1=12
and P3=4. (2)WATER CONTENT OF ACCUMULATOR From the steam flow graph, let us
see the shaded area of "CHARGE" and "DISCHARGE". The biggest valley happens
at 6:00 am which is the total area of (a) and (h). After observing the shaded
area of charge and discharge, we can conclude area (a) + (h) = about 4.1-4.2
ton of steam. With some allowance, say we need to charge 4.5 ton of steam .
Then we will calculate the estimated water content as; 4500 / 69 = about 65
M3. If the water occupies 90% of the vessel, the the vessel volume will be;
65/ 0.9 = 72.2 M3. 3) SIZE OF THE ACCUMULATOR VESSEL Let us use the dish end
plate of 3000 mm diameter. Then the length of the vessel is computed as; 72.2
/ 3.14(1.5 x 1.5) = 10.22 M ACTUAL DIMENSION OF THE ACCUMULATOR............3000
mm dia. x 10000 mm L (4) DISCHARGING SPEED From Fig.-(6), we now calculate
the discharging speed as follows; Max. rate of discharge in Kg of steam /M2
of water surface/ Hour 208.23 x (P3 + 1) = 208.23 x 5 = 1041.15 Kg/M2/H We
get now the available water surface inside the vessel from Fig.-(7). Water
surface: (D x L) x 73% =3 x 10 x 0.73 =21.9 M2 Rate of discharge: 21.9 M2 x
1041.15 =22,801.18 Kg/H In this case, fully stored steam of 4.5 ton will be
discharged at the P3=4 Kg/cm2 pressure with the speed of; (4500 / 22801) x
60= 0.1973 x 60 = 11.8 min. (5) FORMULA:(SUMMARY) In order to unify the value
of steam table, from now on we shall use the value given in the 5 pages of
steam table attached to this documents. D : 3 Diameter of the Vessel ( M) L
: 10 Length of the Vessel (M) V : 70.65 Volume of Vessel (M3) P1 : 12 Initial
Pressure (Kg/cm2) P2 : 4-12 Pressure of the Vessel (Kg/cm2) P3 : 4 Discharge
pressure (Kg/cm2) X : 5545.7 Maximum Charging Capacity (Kg) z : 6029.3 Total
steam flashed at P3 (Kg) S : 21.9 Water surface (M2) w : 63.585 Volume of water
inside vessel (M3) W :w + y 69130.7 Weight of Water at P1 (Kg) h1' : 193.22
Sensible heat at P1 (Kcal/Kg) h3' : 152.13 Sensible heat at P3 (Kcal/Kg) h1" :
502.95 Latent heat at P1 (Kcal/Kg) h3" : 471.13 Latent heat at P3 (Kcal/Kg)
h1 : 664.34 Total heat at P1 (Kcal/Kg) h3 : 655.08 Total heat at P3 (Kcal/Kg)
CHARGING: Water at the P3 pressure can take how many Kg of steam of P1 pressure.
x : (w x h3') + ( x x h1) = (w + x) h1' (63,585 x 152.13) + 664.34 x = (63,585
x 193.22) + 193.22x x(664.34 - 193.22) = 63,585 ( 193.22 - 152.13) x x (Latent
Heat at P1) = 63,585 x ( Sensible Heat P1 - P3) x = 2612707.6 / 471.12 = 5545.7
Kg DISCHARGING: How many Kg of steam can be discharged by Pressure drop of
P1 - P3 z : (w + x) x ( h1' - h3') / h3"( Latent heat at P3) (63,585 + 5545.7)
x ( 193.22 - 152.13) / 655.08 69130.7 x 41.09 / 471.13 = 6,029,29 Kg STABLE
STEAM PRESSURE/CONSTANT FLOW RATE FUEL COST SAVING We can operate the boiler
at a certain pressure and flow rate and maintain it all the time regardless
of the fluctuating demand from the processing line. Boiler operating at the
stable pressure has at least 5% higher boiler efficiency than the boiler operating
with the fluctuating pressure.. This is a direct fuel cost saving and will
reflect immediately to your oil bill. ELECTRICITY COST SAVING Usually coal
fired boiler is equipped with bigger electric motors for its forced and suction
fan which are running through always regardless of the steam flow produced
by the boiler. It is very clear that a lot of electricity loss will incur with
the boiler operating at the very low output than its normal rating. LEVEL UP
THE QUALITY OF YOUR PRODUCT Needless to say that the stable steam pressure
will improve your processing efficiency as well as the quality of your product.
LOWER INVESTMENT ON BOILER UNIT Most of our clients are deciding on the capacity
of boiler based on the expected peak load. With accumulator, you may choose
the boiler capacity based on the average load, thus your investment cost, maintenance
cost, operating cost and fuel cost will be lower than those of the bigger capacity
boiler which is operating with fluctuating pressure and flow rate. ALL TIME
STEAM RESERVE CO-GENERATION Specially when the boiler is used for Back-pressure
turbine for co-generation, for every shut-down of the plant, power load persists
for several hours longer than the process steam load. Electricity load will
continue for offices, lightnings, canteen, kitchen etc., after shut-down of
the processing lines. It is very convenient to be able to store the resulting
exhaust steam that would have to be wasted. Without Accumulator, those exhaust
steam after shut-down of process lines should be wasted to the air. HOLIDAY
/ BOILER MAINTENANCE DAY Boiler operator can easily arrange things that the
accumulator is fully filled/charged with steam before shut-off the boiler so
that the stored steam can be used for many purposes on Sunday, Holidays such
as heaters, kitchen, steam air-conditioning for office( explained later) etc.
without operating the boiler. Stored steam can still be useful even after 8
days of rest ( see Fig.-10). GREAT SAVING BY STEAM-AIR CONDITIONING(Absorption
Chiller) Lithium Bromide air-conditioning( Absorption Chiller) uses heat from
steam as energy to cool offices, factory and cold storage of vegetables/fruits.
When coal fuel is used for the steam boiler, cost of air-conditioning will
go down to 50% of that from the electricity using compressor system. For example,
2,000 m2 office building equipped with Absorption Chiller steam air-conditioning
system of 200,000 Kcal/H-240 KW capacity consumes only 340 Kg ( 0.34 ton) of
steam per hour( pressure at 5 Kg/cm2). With accumulator purposely installed
for this, will give you huge benefit and cost saving. You can always have very
comfortable air-conditioned office, rooms, dormitory, kitchen even without
boiler operating. Such steam in the accumulator should have been stored from
the main of the steam line whenever process steam pressure rises. That means
the accumulator catches energy from the boiler very effectively to prevent
the boiler pressure rise which will cause a great energy loss. Steam accumulated
by these process could cost you very much lower than the cost of process steam.
Figure discussed before is 50% savings when process steam generated from coal
is used for air-condition. Now, If steam from the accumulator is used, saving
rate would be much higher than 50% depending on how efficiently the accumulator
would catch the energy which might have been wasted. SUMMARY Now, you are fully
aware of the SENSIBLE HEAT and LATENT HEAT. "We can only be benefited by the
use of the LATENT HEAT and not the SENSIBLE HEAT as long as the processing
heat is concerned." Let me repeat again and again that when pressure drops
SENSIBLE HEAT of water at the initial pressure must release some heat to reduce
to the level of the SENSIBLE HEAT of the lowered pressure. And when the pressure
rises SENSIBLE HEAT of the initial pressure must gain more heat to match the
SENSIBLE HEAT of the increased pressure. WHEN RELEASING; Firing continues while
you are not receiving any result of it, as release of heat comes from the energy
contained in the water. At that moment, whole water is exerting effort to release
heat to instantly matching the lowered pressure and can no way to accept any
ADDED HEAT from outside. WHEN GAINING; Water will exert its effort to gain
more heat by receiving ADDED HEAT to match with the increased pressure while
steaming is suspended during this period. This kind of energy is totally useless
for you since you do not get steam during the period and yet you do not need
at all the higher pressure than the normal pressure you want. WHEN FLUCTUATIONS
REPEAT; Since you do not need higher pressure, pressure will tend to lower
again. Then releasing will occur causing loss in fuel and it continues endlessly. |