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. |