SOLARDISTILLWATER–ASAFEEDSTOCKTOINDUSTRIALBOILERS

From:-SRI PRAKASH COLLEGE OF ENGINEERING

STREAM:-CHEMICAL

Participants:-

1.ADABLA KUMAR SANJAY(CHEMICAL)NO:-TRQ321

2.B.VAMSI(CHEMICAL)NO:-TRQ531

3.M.SRIKANTHJACKIE(CHEMICAL)NO:-

SOLAR DISTILL WATER–AS A FEED STOCK TO INDUSTRIAL BOILERSABSTRACT:-There is an important need for clean, pure drinking water in many developing countries. Often water sources are brackish (i.e. contain dissolved salts) and/or contain harmful bacteria and therefore cannot be used for drinking. In addition, there are many coastal locations where seawater is abundant but potable water is not available. Pure water is also useful for batteries and in hospitals or schools. Distillation is one of many processes that can be used for water purification. This requires an energy input, as heat, solar radiation can be the source of energy. In this process, water is evaporated, thus separating water vapour from dissolved matter, which is condensed as pure water. For people concerned about the quality of their municipally-supplied drinking water andunhappy with other methods of additional purification available to them, solar distillation oftap water or brackish groundwater can be a pleasant, energy-efficient option.This water can be used for many purposes.one of it’s industrial application is,”“Distilled water is used as a feed stock for Industrial Boilers.

SOLAR DISTILLATION Introduction There is an important need for clean, pure drinking water in many developing countries. Often water sources are brackish (i.e. contain dissolved salts) and/or contain harmful bacteria and therefore cannot be used for drinking. In addition, there are many coastal locations where seawater is abundant but potable water is not available. Pure water is also useful for batteries and in hospitals or schools. Distillation is one of many processes that can be used for water purification. This requires an energy input, as heat, solar radiation can be the source of energy. In this process, water is evaporated, thus separating water vapour from dissolved matter, which is condensed as pure water. Solar water distillation is a solar technology with a very long history and installations were built over 2000 years ago, although to produce salt rather than drinking water. Documented use of solar stills began in the sixteenth century. An early large-scale solar still was built in 1872 to supply a mining community in Chile with drinking water. Mass production occurred for the first time during the Second World War when 200,000 inflatable plastic stills were made to be kept in life-crafts for the US Navy. There are a number of other approaches to water purification and desalination, such as photovoltaic powered reverse-osmosis, for which small-scale commercially available equipment is available. These are not considered here. In addition, if treatment of polluted water is required rather than desalination, slow sand filtration is a good option. The purpose of this technical brief is to provide basic information and direct the reader to other, more detailed sources. Energy requirements for water distillation The energy required to evaporate water is the latent heat of vaporisation of water. This has a value of 2260 kilojoules per kilogram (kJ/kg). This means that to produce 1 litre (i.e. 1kg since the density of water is 1kg/litre) of pure water by distilling brackish water requires a heat input of 2260kJ. This does not allow for the efficiency of the heating method, which will be less than 100%, or for any recovery of latent heat that is rejected when the water vapour is condensed. It should be noted that, although 2260kJ/kg is required to evaporate water, to pump a kg of water through 20m head requires only 0.2kJ/kg. Distillation is therefore normally considered only where there is no local source of fresh water that can be easily pumped or lifted. How a simple solar still operates Figure 1 shows a single-basin still. The main features of operation are the same for all solar stills. The incident solar radiation is transmitted through the glass cover and is absorbed as heat by a black surface in contact with the water to be distilled. The water is thus heated and gives off water vapour. The vapour condenses on the glass cover, which is at a lower temperature because it is in contact with the ambient air, and runs down into a gutter from where it is fed to a storage tank. Solar distillation Practical Action 2

Figure 1: single-basin still

Design objectives for an efficient solar still For high efficiency the solar still should maintain: • a high feed (undistilled) water temperature • a large temperature difference between feed water and condensing surface • lowvapour leakage. A high feed water temperature can be achieved if: • a high proportion of incoming radiation is absorbed by the feed water as heat. Hence low absorption

glazing and a good radiation absorbing surface are required

• heat losses from the floor and walls are kept low • the water is shallow so there is not so much to heat. A large temperature difference can be achieved if: • the condensing surface absorbs little or none of the incoming radiation • condensing water dissipates heat which must be removed rapidly from the condensing surface by, for

example, a second flow of water or air, or by condensing at night.

General arrangement

Design types and their performance Single-basin stills have been much studied and their behaviour is well understood. Efficiencies of 25% are typical. Daily output as a function of solar irradiation is greatest in the early evening when the feed water is still hot but when outside temperatures are falling. Material selection is very important. The cover can be either glass or plastic. Glass is considered to be best for most long-term applications, whereas a plastic (such as polyethylene) can be used for short-term use. Sand concrete or waterproofed concrete are considered best for the basin of a long-life still if it is to be manufactured on-site, but for factory-manufactured stills, prefabricated ferro-concrete is a suitable material. Multiple-effect basin stills have two or more compartments. The condensing surface of the lower compartment is the floor of the upper compartment. The heat given off by the condensing vapour provides energy to vaporize the feed water above. Efficiency is therefore greater than for a single-basin still typically being 35% or more but the cost and complexity are correspondingly higher. Solar distillation Practical Action 3 Wick stills - In a wick still, the feed water flows slowly through a porous, radiation-absorbing pad (the wick). Two advantages are claimed over basin stills. First, the wick can be tilted so that the feed water presents a better angle to the sun (reducing reflection and presenting a large effective area). Second, less feed water is in the still at any time and so the water is heated more quickly and to a higher temperature. Simple wick stills are more efficient than basin stills and some designs are claimed to cost less than a basin still of the same output.

Emergency still - To provide emergency drinking water on land, a very simple still can be made. It makes use of the moisture in the earth. All that is required is a plastic cover, a bowl or bucket, and a pebble. Hybrid designs - There are a number of ways in which solar stills can usefully be combined with another function of technology. Three examples are given: • Rainwater collection. By adding an external gutter, the still cover can be used for rainwater collection to

supplement the solar still output. • Greenhouse-solar still. The roof of a greenhouse can be used as the cover of a still. • Supplementary heating. Waste heat from an engine or the condenser of a refrigerator can be used as

an additional energy input.

Figure 2: simple types of solar stills. Output of a solar still An approximate method of estimating the output of a solar still is given by:

Q = E x G x A 2.3

where: Q = daily output of distilled water (litres/day) E = overall efficiency G = daily global solar irradiation (MJ/m²) A = aperture area of the still ie, the plan areas for a simple basin still (²) Solar distillation Practical Action 4

In a typical country the average, daily, global solar irradiation is typically 18.0 MJ/m² (5 kWh/m²). A simple basin still operates at an overall efficiency of about 30%. Hence the output per square metre of area is:

daily output = 0.30 x 18.0 x 1 2.3

= 2.3 litres (per square metre) The yearly output of a solar still is often therefore referred to as approximately one cubic metre per square metre. Would a solar still suit your needs? Human beings need 1 or 2 litres of water a day to live. The minimum requirement for normal life in developing countries (which includes cooking, cleaning and washing clothes) is 20 litres per day (in the industrialised world 200 to 400 litres per day is typical). Yet some functions can be performed with salty water and a typical requirement for distilled water is 5 litres per person per day. Therefore 2m² of still are needed for each person served. Solar stills should normally only be considered for removal of dissolved salts from water. If there is a choice between brackish ground water or polluted surface water, it will usually be cheaper to use a slow sand filter or other treatment device. If there is no fresh water then the main alternatives are desalination, transportation and rainwater collection. Unlike other techniques of desalination, solar stills are more attractive, the smaller the required output. The initial capital cost of stills is roughly proportional to capacity, whereas other methods have significant economies of scale. For the individual household, therefore, the solar still is most economic. For outputs of 1m³/day or more, reverse osmosis or electrodialysis should be considered as an alternative to solar stills. Much will depend on the availability and price of electrical power. Solar distillation Practical Action 5 For outputs of 200m³/day or more, vapour compression or flash evaporation will normally be least cost. The latter technology can have part of its energy requirement met by solar water heaters.

Fig.2. Isometric View of the Solar Water DistillerDesign SpecificationsThe Distiller is made of the following parts:1. Tempered Glass PlateGlass has the property of selectively allowing only the higher energy radiation topass through and blocking the longer wavelengths. This particular property aidsin the distiller as it captures most of the incoming higher energy radiation butdoes not allow it to radiate back. This also serves as a condensing surface beingopen to atmosphere it will always be at a lower temperature than the waterinside. It is made slanting so that any water droplets that are formed finally movealong the gradient where they finally deposit the condensate into collector.2. Top water reservoirWater is stored on top just under the glass plate. This water needs to berecharged everyday. The floor of the container is painted black to maximize theirradiation capture. The paint needs to be not water soluble and dried in sun

In many parts of the world, fresh water is transported from another region or location by boat, train, truck or pipeline. The cost of water transported by vehicles is typically of the same order of magnitude as that produced by solar stills. A pipeline may be less expensive for very large quantities. Rainwater collection is an even simpler technique than solar distillation in areas where rain is not scarce, but requires a greater area and usually a larger storage tank. If ready-made collection surfaces exist (such as house roofs) these may provide a less expensive source for obtaining clean water. For the purpose of design we will assume a very low conversion efficiency of around 20%.Given the highly erratic supply of sunlight which depends greatly on weather conditions wehave to over design it for high factor of safety – in this case 2. In real life we expect theefficiency to be higher than 40%.The first step in design is to calculate the aperture area.Aperture Area = Energy required for distillation of 30 liters of water / Solar energyavailable per m2 * conversion efficiency= (30 kg/day * 4.2kJ/kg oC * (60-30) oC)/(1 kW/m2 * 3600 s/hour *6hours/day)*(0.2)= 0.8 m2

So we need total area of 0.8 m 2 for the distillation of 30 liters of water daily.

INTRODUCTION TO BOILERSA boiler is an enclosed vessel that provides a means for combustion heat to be transferred intowater until it becomes heated water or a gas (steam). The steamor hot water under pressure is then usable for transferring the heatto a process. Water is a useful and cheap medium for transferring

heat to a process. When water is boiled into steam its volumeincreases about 1,600 times, producing a force that is almost asexplosive as gunpowder. This causes the boiler to be anextremely dangerous item that must be treated with utmostrespect.Boilers were used in crude fashions for several centuries butdevelopment was slow because construction techniques werecrude and the operation was extremely dangerous. But by theindustrial revolution of the mid 1800’s boilers had become themain source of energy to power industrial operations andtransportation. The use of water as a heat transfer medium hasmany advantages. Water is relatively cheap, it can be easilycontrolled, the gas in invisible, odorless, and extremely high purity.The process of heating a liquid until it reaches it's gaseous state is called evaporation. Heat istransferred from one body to another by means of (1) radiation, which is the transfer of heatfrom a hot body to a cold body through a conveying medium without physical contact, (2)convection, the transfer of heat by a conveying medium, such as air or water and (3)conduction, transfer of heat by actual physical contact, molecule to molecule. The heatingsurfaceis any part of the boiler metal that has hot gases of combustion on one side and wateron the other. Any part of the boiler metal that actually contributes to making steam is heatingsurface. The amount of heating surface a boiler has is expressed in square feet. The larger theamount of heating surface a boiler has the more efficient it becomes. The measurement of thesteam produced is generally in pounds of water evaporated to steam per hour.Gallons of water evaporated x 8.3 pounds/gallon water = Pounds of steamIn firetube boilers the term boiler horsepower is often used. A boiler horsepower is 34.5

pounds of steam. This term was coined by James Watt a Scottish inventor. The measurementof heat is in British Thermal Units (Btu’s). A Btu is the amount of heat required to raise thetemperature of one pound of water one degree Fahrenheit. When water is at 32 oF it isassumed that its heat value is zero.

SENSIBLE HEAT:-

The heat required to change the temperature of a substance iscalled its sensible heat. In the teapot illustration to the left the 70oF water contains 38 Btu’s and by adding 142 Btu’s the water isbrought to boiling point.In the illustration to the left, to change the liquid (water) to itsgaseous state (steam) an

LATENT HEAT

additional 970 Btu’s would berequired. This quantity of heat

required to change a chemicalfrom the liquid to the gaseousstate is called latent heat.The saturation temperature or boiling point is a function ofpressure and rises when pressure increases. When waterunder pressure is heated its saturation temperature risesabove 212 oF. This occurs in the boiler. In the example belowthe boiler is operating at a pressure of 100 psig which gives asteam temperature of 338 oF or 1185 Btu’s.When heat is added to saturated steam out of contact withliquid, its temperature is said to be superheated. Thetemperature of superheated steam, expressed as degrees above saturation, is referred to as thedegrees of superheat.BOILER TYPES:There are virtually infinite numbers of boiler designs but generallythey fit into one of two categories: (1) Firetube or as an easy wayto remember "fire in tube" boilers, contain long steel tubes throughwhich the hot gasses from a furnace pass and around which thewater to be changed to steam circulates, and (2) Watertube or"water in tube" boilers in which the conditions are reversed with thewater passing through the tubes and the furnace for the hot gassesis made up of the water tubes. In a firetube boiler the heat (gasses)from the combustion of the fuel passes through tubes and istransferred to the water which is in a large cylindrical storagearea. Common types of firetube boilers are scotch marine, firebox,HRT or horizontal return tube. Firetube boilers typically have alower initial cost, are more fuel efficient and easier to operate butthey are limited generally to capacities of 50,000pph and pressures of 250 psig. The morecommon types of watertube boilers are "D" type, "A" type, "O" type, bent tube, and cast-ironsectional. All firetube boilers and most watertube boilers are packaged boilers in that they canbe transported by truck, rail or barge. Large watertube boilers used in industries with largesteam demands and in utilities must be completely assembled and constructed in the field andare called field erected boilers.

Firetube Scotch Marine Boiler

Watertube Boiler D-Type

Watertube Boiler "A Type"

Vertical tubeless boilers are used for small loads but really do not fit into either category as theydo not have tubes.Boilers and pressure vessels are built under requirements of the American Society of

Mechanical Engineers or ASME referred to as the "ASME Code." High pressure boilers arefired vessels for an operation greater than 15 psig and 160oF and are built in accordance withSection I of the ASME Code with the ASME S stamp. Vessels with design pressures below 15… The water supplied to the boiler that is converted into steam is called feedwater. The twosources of feedwater are: (1) Condensate. or condensed steam returned from the processesand (2) Makeup water (usually city water) which must come from outside the boiler room andplant processes. For higher boiler efficiencies the feedwater can be heated, usually byeconomizers.

\

MAKEUP WATERA. WATER SOFTENERS:Water as it passes over the ground, through caves and springs picks up some of the elementsfrom the limestone and other elements of nature which dissolved and remain. These elementscollectively are called hardness. Grandma's tea kettle, used as an example in Chapter One,always seemed to have a "build up" in the bottom which she removed periodically usually withvinegar. This "build up" is called hardness. In a heavy use industrial steam boiler the water iscould be completely replaced as often as once each hour. Obviously at higher turnover,temperatures and pressures than the tea kettle the boiler would quickly have scale from thishardness that would reduce and ultimately prevent water circulation and heat transfer which will

destroy the boiler. The higher the operating pressure of the boiler the more critical the removalof foreign items from the feedwater becomes. Large utility boilers operating at 3,000 psig + mayactually use distilled water for ultimate purity.The purpose of a water softener is primarily for the removal of hardness from the boiler makeupwater. Makeup water is the water supplied from the municipal water system, well water, orother source for the addition of new water to the boiler system necessary to replace the waterevaporated. Some filtering of the water may occur in the water softener but that is not thepurpose of its design and too much of other pollutants in the water could actually foul the watersoftener affecting its operation. Hardness is composed primarily of calcium (Ca) andmagnesium (Mg) but also to lesser amounts sodium (Na), potassium (P), and several othermetals. Hardness is measured in grains with one grain of hardness in the water being 17.1 ppmof these elements. The purpose of using hardness as the unit of measure is that tests tomeasure in parts per million (ppm) are much more difficult and expensive to use. Hardnessvaries from area to area. Usually near salt water the hardness is very low as the limestone isvirtually non existent and in mountainous areas where limestone is everywhere hardness isusually very high.All softeners soften or remove the hardness from the water. The primary minerals in the waterthat make "hard" water are Calcium (Ca++) and Magnesium (Mg++). They form a curd withsoap and scale in piping, water heaters and whatever the hard water contacts. Hardness isremoved from the water by a process known as positive ion exchange. This process could alsobe known as "ion substitution", for substitution is what occurs. Sodium (Na+) ions, which are"soft" are substituted or exchanged for the Calcium and Magnesium as the water passes throughthe softener tank.The softening media is commonly called resin or Zeolite. The proper name for it is polystyreneresin. The resin has the ability to attract positive charges to itself. The reason it does so is

because in its manufacture it inherits a negative charge. It is a law of nature that oppositecharges attract, i.e., a negative will attract a positive and vice versa. A softener tank containshundreds of thousands of Zeolite beads. Each bead is a negative in nature and can be chargedor regenerated with positive ions. In a softener, the Zeolite is charged with positive, "soft" sodiumions.As "hard" water passes through the Zeolite, the Calcium and Magnesium ions are stronglyattracted to the beads. As the "hard" ions attach to the Zeolite bead, they displace the "soft"Sodium ions that are already attached to the bead. In effect, the Sodium is "exchanged" for the Calcium and Magnesium in the water supply with the Calcium and Magnesium remaining on theZeolite beads and the Sodium ions taking their place in the water flowing through the softenertank. The result of this "exchange" process is soft water flowing out of the tank.It can now be readily understood that a softener will continue to produce "soft" water only aslong as there are Sodium ions remaining on the Zeolite beads to "exchange" with the Calciumand Magnesium ions in the "hard" water. When the supply of Sodium ions has been depleted,the Zeolite beads must be "regenerated" with a new supply of Sodium ions. The regeneration ofthe Zeolite beads is accomplished by a three step process.SOFTENER DESIGN:Water softeners come as single mineral tank units (simplex), double mineral tank units (duplex)and multiple mineral tank units. Since regeneration cycles can take approximately one hoursimplex units are used only when this interruption can be tolerated. To avoid interruption duplexunits are used so that the regeneration of one unit can be accomplished while the second unit ison line. Triplex or other multiplex units usually are the result of need for increased capacity andunits can be added to keep soft water available. The reliability of new electronicmetering/controls for regeneration have allowed users to depend on smaller units with morefrequent regeneration.

Simplex Softener Duplex Softener Triplex Softener

REGENERATION PROCESSBACKWASH:The flow of water through the mineral bed is reversed. The mineral bed is loosened andaccumulated sediment is washed to the drain by the upward flow of the water. An automaticbackwash flow controller maintains the proper flow rate to prevent the loss of resin.BRINE DRAW AND SLOW RINSE:Ordinary salt has the capability to restore the exchange capacity of the mineral. A given amountof salt-brine is rinsed slowly through the mineral bed. After the salt-brine is drawn, the unit willcontinue to rinse slowly with water to remove all of the salt-brine from the media bed.FAST RINSE:A high down flow of water repacks the mineral bed. Any trace of brine not removed in slow rinseis flushed to the drain.The unit is then returned to SERVICE the brine maker is refilled with fresh water to form saltbrine for the next regeneration. The total regeneration time is approximately 60-90 minutesSOFTENER SIZING FORMULA:

C = M * T * H /RC = Capacity of softener in cubic feet of resinM = Makeup water volume per hour in gallons; the volume needed to be softened (8.34 poundsper gallon)T = Time in hours desired between regeneration cyclesH = Hardness of water in grains (17.1 ppm per grain hardness)R = Resin Capacity per cubic foot (this is virtually always 30,000 grains

Feeding chemicals into the system can be done using several methods or a combination ofmethods. Continuous feed pumps are the best and most reliable method for high pressure steamsystems. Continuous feed pumps offer a smooth, even flow of chemicals without high or lowswings or residual. To get the best performance and reliability, the feed pumps must be properlyset-up and adjusted as the need varies. A typical system uses a pump to feed treatment chemicalsinto the steam drum or in the boiler feedwater line. Another feed pump injects amine into thesteam header using stainless steel quills, and a third pump injects an oxygen scavenger into thedeaerator

Further information • Malik A S et al - 'Solar Distillation' - Pergamon Press - 1982. Provides a comprehensive technical text. • Waterlines Journal Volume 7 No 2. Developing Appropriate Technologies in Peru 1988.

Useful Addresses

ISES - International Solar Energy Society Burkhard Holder, Director Ryan van Staden Christopher Findlay Villa Tannheim, Wiesentalstrasse 50 D-79115 Freiburg Germany Tel: +49 761 459 060 Fax: +49 761 459 0699 E-mail: hq@ises.org Website: http://www.ises.org

International Desalination Association (IDA) POB 387 37 Main St. Topsfield, MA 01983 USA Tel: +1 508 887 0410, 356 27 27 Fax: +1 508 887 0411 idalpabgix.netcom.com http://www.ida.bmThe goals of the Association are the development and promotion of the appropriate use of desalination (the method of removing salts and other impurities from water) and desalination technology worldwide.

Indian Desalination Association (InDA) Dr. B.M. Misra Mumbai 400 085 India Tel: +91 22 5513992 / 5563060 Ext. 4705 /4706 Fax: +91 22 5560750 bmmisra@magnum.barctl.ernet.in www.buc.emet.in An affiliate of IDA

Pakistan Desalination Association (PaKDA) 42, Bhayani Centre, Block-M North Nazimabad, Karachi Pakistan Tel: + 92 21 6677341-2 Fax: + 92 21 6641121 nahmed@paknet3.ptc.pk An affiliate of IDA