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Hamada Boiler
Hamada Boiler Group Head Office
Hangzhou, Zhejiang Province, China
Tel: +86-571-87655979, 87655989
Fax: +86-571-87655969
Steam Accumulator |Products | Home |
As far as steam for heating and process is concerned, there are just two fundamental things that govern everything;
    1. The boiling point of water decreases with reduced pressure.
    2. The latent heat (the "heating heat) of steam increases with reduced pressure

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.

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 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.

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.

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".

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".

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.

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.

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.

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.

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.










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.

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