Gordon Trucking Inc. GTI stands out in the Services category for its commitment to reducing emissions and increasing fuel efficiency of its 1,truck fleet of Class 8 freight tractors. Last year, the south Puget Sound trucking giant installed filtration technology that reduced oil waste by 27, gallons annually. By decreasing the maximum speed of its trucks from 65 mph to 60 mph, the company will save 1 million gallons of fuel per year.
GTI has also added more efficient auxiliary power units APUs to of its trucks, which have reduced idling time from 20 percent to 12 percent. The intent is to outfit the remainder of the fleet with APUs in the next three years and to purchase around new clean-burning trucks this year. All told, GTI's emissions reductions efforts have led to the elimination of , tons of carbon dioxide, 1, tons of particulate matter and tons of nitrous oxides from the skies every year, says Kirk Altrichter, GTI's vice president of maintenance.
The runner-up, the luxury Hotel Monaco-Seattle monaco-seattle. The hotel has maintained an 86 percent recycling rate and a 60 percent reduction in restaurant waste through a food composting program. OF NOTE: Another standout was Seattle's Brown Bear Car Wash , which has provided more than , free car wash tickets to schools and over charity groups so they can hold fundraising events at Brown Bear's facilities, where effluent can be properly processed and disposed of, and prevented from reaching waterways.
This year, the Green Washington judges happily noted that many major utilities were making strides in energy savings. Puget Sound Energy PSE , however, breezed ahead by a nose due to its extensive investments in alternate fuel sources and its continued leadership in wind and solar project development. PSE, the nation's second-largest utility owner of wind power generation facilities, meets the electricity needs of about , customers with the Hopkins Ridge and Wild Horse wind facilities. PSE has also built a 2,panel solar project, the largest in the Northwest, at the Wild Horse facility.
As the first utility in the country to be "greenhouse gas neutral" via renewable fuel and purchasing offsets, City Light's conservation program has prevented , metric tons of CO 2 from being released and saved enough energy in to power , homes for one year. Seattle-based McKinstry edged out a field of 20 impressive, forward-thinking architectural and construction firms that have adopted the Leadership in Energy and Environmental Design LEED building standards developed by the U. S Green Building Council. Because office buildings account for about half of the greenhouse gases produced in the United States, the green building movement has the potential to make one of the most noticeable impacts on reducing cities' carbon footprints.
A recent study by Gardner-Johnson also found that residential homes certified by King and Snohomish counties' Built Green program have increased in value by about 2 percent from to in east King County, while the value of uncertified homes decreased by 2 percent during the same period. For projects completed in and alone, emissions reductions at McKinstry buildings included 55 million pounds of carbon dioxide, 65, pounds of nitrous oxides, 18, pounds of sulfur dioxide and 2, pounds of carbon monoxide.
Seattle-based architecture and urban design firm GGLO gglo. A champion of incorporating sustainable elements in affordable housing projects, GGLO has also designed more than 1, green residential units. Sellen Construction in Seattle recycles 91 percent of its construction waste on its projects, 90 percent of which are LEED certified.
For many retailers, being green means merely complying with new environmental regulations. But for those progressive retailers in the upper echelons of the ecological movement, such as Seattle's homegrown PCC Natural Markets chain, being green is part of their core identity-a bar that is raised each time it is met. With each new store built by this organic and natural foods grocery chain, PCC sets a new standard for its own conservation and green building goals.
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Beginning in , PCC's initial Green Lake neighborhood store included a produce-composting program, low-VOC paints, cork linoleum flooring and tabletops made of recycled fibers. In , the Fremont store added high-efficiency lighting, photovoltaic panels, cabinetry made of recycled materials, and an integrated hot water, HVAC and refrigeration system.
Three years later, the Redmond store was the first-ever grocery store to meet stringent LEED Gold certification standards. This fall, PCC's new store, which opened earlier this year in Edmonds, is expected to earn LEED Platinum status for its green elements, including specially glazed windows to block out 65 percent of the sun's heat, LED lighting that will use 25 percent of the energy needed for incandescent bulbs, and a rainwater collection system capable of handling , gallons annually.
PCC expects the Edmonds store to outperform industry energy standards by at least 50 percent, says Diana Crane, the chain's director of sustainability. Not only has Pagliacci instituted a composting program for its food waste, pizza boxes and 95 percent of its packaging, but it also established an educational campaign that displayed conservation facts, tips and contact information on all of its pizza boxes, and partnered with Seattle Public Utilities in to create radio and TV public service announcements about recycling food waste at home.
Old-school market capitalists may scoff at the idea of a "not-for-profit" organization having power over the local economy, but some of these groups have had a major impact on state and regional policy in recent years. For instance, as one of the top global-warming political action groups in the Pacific Northwest, Climate Solutions successfully led a coalition of business leaders to help pass the landmark Climate Action and Green Jobs initiative HB , says Ethan Schaffer, director of major gifts and grants at Climate Solutions.
The signing of HB last year makes Washington the fourth state in the nation to put a cap on greenhouse gas emissions with a target of returning to levels or below by , 25 percent below levels by and 50 percent below levels by The legislation also makes Washington the only state to create a training program for the expected tripling of new jobs in wind, solar and geothermal energy generation by , Schaffer says.
In recent years, GSI has created a business-focused group called the Consortium of Leading Energy and Efficiency Northwest CLEEN , made presentations on incentives to help offset the cost of including energy-efficient improvements at businesses and developed partnerships to promote sustainable building practices in Spokane.
OF NOTE: Another economic development group, enterpriseSeattle , which helped found the Washington Clean Technology Alliance trade association, has provided free development assistance to more than emerging clean-tech companies, helping to create more than 1, family-wage jobs. The Seattle Art Museum , the only such institution to employ a full-time environmental steward, redeveloped a brownfield site and restored part of the city's shoreline habitat during construction of its Olympic Sculpture Park, which features mostly native flora, reduces stormwater runoff, and uses no pesticides.
The penguin exhibit at the Woodland Park Zoo recirculates and cleans its water every 36 minutes. Solution : The expansion lines and engine efficiencies of Example 7 were on the overall basis. In order to estimate the ex- traction performance it is necessary to estiirate the mech- anical and generator efficiencies and to replot the expan- sion lines. Church, E. Gardner, F. Newman, L.
An Introduction to Prime Movers for Auxiliary Power Systems
Warren, G. Condenser s--The purpose of the condenser in a vapor cycle is prirrarily to lower the temperature of the prime mover exhaust so that the thermal efficiency of the cycle can be increased. Operation of condensers at sub-atmospheric pressures requir- es the use of vacuum pumps to remove the air which unavoid- ably leaks into the condenser and which, if not remioved, would make it impossible to maintain the lew exhaust temper- ature.
Condensers may be divided into two general classes: mixing condensers and surface condensers. The most import- ant type is the surface condenser which allows the reduction of exhaust temperature while at the same time allowing the recovery of the condensate.
The mixing condenser is able only to lower the exhaust temperature without recovering the c ondensate.
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The jet type de- pends upon the aspirating action of a jet of water to con- dense the steam and to remove the air from the condenser. A typical jet condenser is shown in Figure VI The use of the jet for aspirating air requires more pump power for a given vacuum, but a separate vacuum pump is not required. The bar- ometric condenser utilizes a leg of water to provide the seal for the condenser rather than power from a pump as in the jet condenser. The barometric condenser is always provid- ed with a vacuum pump for air remioval.
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A typical barometric condenser is shown in Figure VI— 2. With 70 P cooling water, about the best vacuum which can be maintained with a mtixing condenser is 28 inches of mercury. Due to the fact that the volume of the condenser is small in relation to the amount of steami and water handled, the mixing process does not reach equilibrium and the temperature of the mixture leaving the condenser will be about 5 P less than the saturation temper- ature corresponding to the pressure in the condenser.
Surface Condenser s--The surface condenser has the ad vantage of making it possible to save the condensed steam for use as boiler feed, but keeping the condensing steam separate from the cooling water requires that the heat be transferred through a dividing wall. This necessity complicates the de- sign of condensers by making it necessary to take into ac- count the resistance of the dividing wall to heat flow.
Surface condensers will be made in as many shapes and designs as there are manufacturers, the only sirrilmrity be- ing in the existence of water boxes, tubes, a shell and a iiotwell. Figure VI— 3 shows a typical surface condenser with its various parts. Figure VI-4 shows the heat paths in re- lation to a conventional condenser tube in which the tube conveys the cooling water and is surrounded by the steam. Temperature relations in heat transfer through condenser tube. The outside and inside diameters of the tube are the only definitely measureable distances in the heat path.
U 4 4s 4 1 K tt u As previously mentioned, the only readily determined dimensions are the inside and outside diameters of the tube. Furthermore, the area of condensing surface is always meas- ured on the outside diameter of the tube. For these reasons all areas are corrected to the outside area of the tube, so that if all elements in the heat flow path except the tube are considered to have no thickness. TiC, D, 4 1 tt a where: and D. Table VI shows approximate values of K for several mat- erials which are commonly used for heat transfer surfaces.
For purposes of estimation, h for the scale may be taken as ranging between for favorable con- ditions and for unfavorable conditions, with an average of about 3C0C. After having found the vallie of U for the condenser, the total surface required may be found from the relation. BWG in. This diff- erence in temper- ature is called the terminal difference, and is usually from 5 to 1C F for surface condensers, the smaller applying to two pass and the larger to single pass de- signs, Refrig- eration or reheating according to the design of the conden- ser is encountered with the water leaving the hotwell.
This action will have to be taken into account in the computation of the heat transferred, but it must be ignored in the com- putation of the mean temperature difference because of the smallness of the effect of removal of sensible heat in the condenser. In well designed condensers refrigeration will not exceed 5 F, and some designs will actually reheat as much as 2 F. Tcipperaturt relations In tranafer through condenser tube.
Example 9 shows the method of calculating the principal dimxensions of a surface condenser for the regenerative cycle of Example 8. Example 9. Estimate the principal dimensions of a surface conden- ser to serve the turbine of Example 8. Inlet cooling water temperature 72 F, terminal difference 8 F.
The temperature of the steam in the condenser is lOl F. Figure VI-6 shows the curves in use for surface condensers. In use, the overall heat transfer coefficient from the curves is reduced by a so-call- ed "cleanliness factor," which is usually taken as about 0. In commercial practice loading ranges from 7 to 10 pounds of steam per square foot per hour.
Example 10 shows the method of application of the Heat Exchange Institute data to the determination of the dimensions of a surface conden- ser for the same duty as in Example 9. Example Estimate the principal dimensions of the condenser of Example 9 by means of the Heat Exchange Institute data. Take the cleanliness factor as 0. Length of tubes 0. Feed-Water Heaters--The primary function of feed- water heaters, is to utilize extracted or exhaust steam from prime movers to increase the temperature of water before feeding it to boilers.
Feed-water heaters may be divided into two general classes: open or mixing and closed or surface heaters. Feed-water heaters are counterparts of condensers, the difference being in their smaller size and higher operating temperature. Open He0ters--T he nane "open heater" often leads to a misconception of the operation of this type of heater. Actually, an epen heater can operate at any pressure, not necessarily atmospheric. All modern regenerative cycles in- clude one open heater in the feed-water circuit, so designed as to act as a scrubber for deaerating the feed-water before it enters the boiler.
Deaeration is necessary to remove oxy- gen and other gases which are harmful to boilers and piping, and which have entered the system by leaking into the conden- ser. It is Quite comm. This stor- age is usually about a two or three minute sup- ply at full load. Often additional surge tanks are connected through overflows and surge pumps with the water storage section of the deaerating heater to provide add- itional ernergercy storage tor unusual conditions. The same consider- ations of heat balance apply to open heaters as to mixing condensers.
Well proportioned deaer- ating heaters will pro— duce water with alirost VI. Closed Heaters — Due to the fact that the water is separated fron the steam in a closed heater, it is possible to operate them at high water pressures in relation to the steam pressure.
The same considerations of heat transfer apply to closed feed-water heaters as to surface condensersL Because feed- water heaters operate with relatively clean tubes, the val- ue of h for scale can be taken to be about Deaign data for doaerating feed-aatcr haatera. Refrigeration in the hotwell of horizontal heaters will be of about the same magnitude as for surface condensers, but will be from 1C to 15 F for vertical heaters.
Water velocities are somewhat smaller than for surface condensers, ranging from 3 to 8 feet per second. Th drainage from closed heaters is usually flashed to the next lower heater in the circuit, while the drainage from the first closed heater Ai.. Closed feed'Vater heater. The heater air offtakes are connected to the condenser through flow limiting orifices. Examp 1 e II. Specify the principal dimensions of a six-pass closed feed—water heater to serve the regenerative cycle of Example 8.
Terminal difference 6 F. The temperature of the steam in the heater is F; water temperature to the heater lOl P and from the heater F. Estinate the area required for the closed feed-water heater of Example 11 by means of the Kittredge data. This area is quite close to the area determined by the method of Example Vacuum Pumps--As previously mentioned, a condenser must be supplied with some sort of air removal apparatus. The usual equipment consists of steam ejectors with suitable coolers, although some plants niake use of mechanic- al air pumps.
The size of the vacuum equip- ment will de- Air to Atvoiphere pend upon the air leakage to be expected. Steam jot vacuum pump. Back Pressure, ir. Steam jet vacuum pump. Fig- ure VI shows the approximate maximum air leakage to be ex- pected , Water Cooling Equipment --Plants must often be located where an abundant source of con- denser cooling water is not available.
In these cases it is necessary to provide a spray pond or cooling tower and to use a closed circuit for the cooling water. Both s pra y po nds. Per Cent of Rated Capacity Fig. Ejector operating characteristic!. Spray ponds are wasteful of ground space because they depend upon natural air motion for their effective operation Cn the other hand, they are relatively inexpensive to oper- ate because they only require enough power to produce a pres sure of about 10 pounds per square inch at the spray nozzles Figure VI shows a spray pond with the nozzles arranged in clusters, each cluster having a capacity of about gallons per minute It can be estimated that a spray pond will require about one square foot of ground area for each pounds per hour of water to be cooled.
The depth of the — j J Kc. Figure VI shows some typical spray pond performance data. Spray ponH performance. The air flows through the falling water drops. Evapor ator s--Sirce regenerative cycles operate with the same water continuously and leakage is slight, it has been found advantageous to use evaporators to produce dis- tilled water tor the small amount of makeup required. Make- up requirements vary from about two to five per cent, depend- ing upon a number of factors such as the amount of boiler blowdown and auxiliary steam unrecovered.
VI, Forced and Induced draft tower performance. It will be noted that the only heat loss from the system is due to the necessary blowdown from the evapor- ator shell. In process industries which perforin evaporation on a product, multiple effect evaporator systems are used because of their economy of operation. It will be noted that the vapor from a proceeding effect is used as a source of heat for successive evaporations.
The evaporators are of the long tube type with vapor separating heads. In this type of evap- orator the liquid flows inside the tubes. In the first four effects the circulation is natural, and in the finishing pan a pump forces circulation. Figure VI shows long tube types of evaporator. Nance, G. Wheeler, P. The power plant of Project I is to be designed around three turbo-generator units.
One of the units will operate continuously, one unit will be operated to handle peak loads and the remaining unit will be a spare. The plant will operate on the regenerative cycle with one closed feed— water heater and one evaporator vapor condenser per. There will be one evaporator and one deaerating feed-water heater common to all machines. Boiler blowdown is fed to the evaporator shell.
The flew diagran is shown in Figure VI It is expected that boiler and evaporator blowdown will each be five per cent and makeup will be two per cent. The open heater and evaporator will be supplied with steam from extraction points in the turbines so located that at full load the water temperature leavirg the open heater will be at the most economical value. The closed heaters will be supplied with steam from extraction points in the turbines so located that at full load half of the feed— water temper- ature rise will be supplied by the open heater.
Throttle conditions are: psig, F. Back pressure is 2. Refrigeration in the condenser hotwell is 2 F and terminal difference in the open heater is zero. Make heat balances for the plant at full and half load two machines operating. Specify the principal dimensions for a surface con- denser to serve one of the turbines of part one. The aver- age temperature of the inlet cooling water is 85 F.
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Specify the area of an induced draft cooling tower to serve the condenser of part two. Design wet bulb temper- ature is 78 F. Specify the principal dimensions of a closed feed- water heater to serve oneof the turbines of part one. Maximum tube length is six feet. Specify the principal dimensions of the deaerating feed-water heater for the regenerative cycle of part one. The variety of fuels used for the production of power is large, and the type used in any particular locality is always dependent upon econoiric factors.
The most import- fuels for commercial power production, in order of import- ance, are: coal, natural gas and fuel oil. Process indus- tries often make use of cellulosic wastes as fuel. Coal --Coal is a product of fermentation of vegetable matter laid down in prehistoric times. In this country, coal is found in almost every State in various phases of the evolutionary process.
The most important coals for power production are the bituminous and semi— bituminous types, but some use is made of lignite and anthracite which are respect- ively younger and older than bituminous coal. Coal is made up of moisture, volatile matter, fixed car- bon and ash. The proportions of moisture and volatile matt- er decrease as the age of the coal deposit increases. Vol- atile matter consists of hydrocarbons which have a greater heating value than carbon on a weight basis, but which are more difficult to burn in small furnace volumes. Table VIII shows the analysis of some of the more important coals, both in the proximate form fixed carbon, volatile, ash and mois- ture and in the ultimate form.
Fuel Oil--The fuel oil ordinarily used in the pro- duction of eleatrical power is residuum from petroleum re- fining opera'tions. Petroleum is found in large areas through the United States and South America, and is also a product of the fermentation of vegetable matter laid down in past ages. Its prircipal difference from coal is the almost com- plete absence of fixed carbon and ash. Table IX shows some analyses of typical fuel oils. The most important sources of fuel oil for the United States are the Pacific and Gulf coasts and Venezuela. Natural Gas--Natural gas is principally a by-prod- uct from petroleum wells, although much gas is removed from the earth's crust through wells which are not connected with petroleum operations.
Natural gas is a product of the fer- mentation of vegetable matter to produce coal and petroleum. Table X shows some analyses for natural gas. CO -si: cc. In order to calculate the amount of air, which is the source of oxygen, for combustion, it is neces- sary to know the ultimate analysis of the fuel. Since the combustion process takes place too rapidly to reach equilib- rium, it is always necessary to supply more than the theo- retical amount of air.
Both total air and excess air are expressed as percentages by weight of the theoretical air. Examples 13 and 14 show the method of making combustion calculations for each of the principal types of fuels. OlO 28 0. Often it is necessary to determine combustion conditions from a fuel analysis and an analysis of the flue gas. Ex- amples 15 and 16 show the method followed for each of the types of fuels. Find the theoretical air, actual air and flue gas produced in lbs per lb of fuel fired.
Solution : 1. If all of carbon in the fuel is not burned a correction is made see Example Find the theoretical air, actual air and flue gas in lbs per lb of fuel fired and the percentage of excess air supplied. Solution: The first step in the solution is the conversion of the volumetric analysis to a gravimetric analysis. Theoretical air: M. Excess air: Heating Value of Fuela--One of the most important properties of any fuel is its heating value per unit of weight or volume. The higher heating value ITHV is the value which would be obtained if the products of combustion were cooled to the temperature of the original fuel and air.
The lower heating value LHV is the higher heating value less the latent heat of vaporization of the moisture formed in the combustion process and present in the fuel originally. It is customary to base efficiencies on the higher heating values, although efficiencies would appear to be higher if they were based on the lower heating value. The heating values of fuels can be determined approx- imately by calculation if the ultimate analysis, proximate analysis for coal or specific gravity for fuel oil is known.
It will be noted that the proximate analysis must be converted to the com- bustible basis before the table is used, and the result con- verted to the as fired basis. The proceeding equations are only approximate, and for the most precise determination of heating value it will be necessary to employ a calorimeter of a suitable type. The Orsat analysis is given on the dry basis be- cause the sample remains saturated with moisture throughout the test proced- ure. It is ass- umed that the remaining gas is nitrogen. Due to the fact that the reagent for carbon dioxide will absorb all acid gases, the sulphur- ous gases in the products of combustion will be analyzed as is slight for ordinary fuels.
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Orsat gas analysis apparatus. Kreisinger, H. Peabody, E. M,E,, Volumes , Philo, F. E,, November, Steam gen- erators are divided into two general classifications: fire -tube and water-tube, depending upon whether the water sur- rounds the tubes or is contained within the tubes.
Steam generators in small sizes are rated in terms of boiler horsepower, which amounts to a heat absorption of 33, Btu per hour per boiler horsepower, or One boiler horsepower is also approximately equal to ten square feet of convection heating surface. Large steam generators are rated in terms of the actual weight of steam produced per hour at definite outlet conditions with feed-water at a definite temperature. This method requires that the flue gas analysis and ultimate analysis of the fuel, as well as combustion air temperature, fuel temperature and flue gas temperature be known.
The various losses per pound of fuel can then be cal- culated and the difference between the heating value of the fuel and the losses considered as the heat absorbed by the steam generator. The losses are! This item can be estimated at from C. The above losses might be regrouped into two general classi- fications, as follows: A.
Combustion losses due to failure to develop the full heating value of the fuel. These items would in- clude items d and e and part of g. Conversion losses due to failure to transmit all of the heat developed to the steam. These losses would include items a , b , c and f and part of g. Example 17 shows the method of determination of steam generator efficiency by the direct method and by the method of losses for solid or liquid fuels, and Example 18 shows the same procedure for gaseous fuels.
Pry gas: See Example 15 M 44 Heat absorbed by boiler: Wt. The following data were recorded for a test on a boiler rated at 25, lbs per hour and equipped with plain brick furnace walls: Average steam pressure psig Average steam temperature F Steam generated in 4 hours 86, lbs Average feed-water temperature P Heating value of gas std. Heat absorbed by boiler: See Example 17 From the calcuJations converting the fuel analysis to the gravimetric basis, the apparent molecular weight is The principal types are: horizontal return tubular; Scotch marine; vertical tubular; and firebox tubular.
Horizontal return tubular boilers consist of a drum with longitudinal flues set over a brick firebox, as shown in Fig- ure VIII— 2. They are moderately efficient and are suitable for use with any kind of fuel. Scotch marine boilers are so named because they were first used in steam powered ships built in Scotland. They have been adapted to stationary power plants and are most popular for packaged units because the furnace is internal to the boiler. Vertical tubular bo'. Due to the fact that part of the flues are above the water line, the steam is delivered with a small amount of superheat.
Their advantage is the ability to put more heating surface in a given total boiler volume than the other fire-tube types. Fire-tube boilers are not made for high pressures be- cause of the difficulty of staying the flat tube sheets against bulging, and because tubes are relatively less re- sistant to collapse from external pressure than they are to rupture from, internal pressure. Water-Tube Bo i I e r s--Water -t ube boilers are built in capacities from about ICC boiler horsepower to more than one million pounds of steam per hour, with pressures ranging from 15 to psig.
The variety of water-tube boilers is very large, but the general types are: straight tube and bent tube. Straight tube boilers require the use of headers for the tube ends. The main disadvantage is that the many hand- rig. The main advantages are that all of the steam generating tubes are alike and they are easy to clean, when neces- sary. Power Flf.
Croat druai atralght tuba bailor. Bent tube boilers were designed to eliirirate the tube headers and handhole covers which gave trouble in the straight tube boilers in the higher pressure ranges. Heat Transfer in Boilers — The major portion of the heat transfer in boilers takes place by convection from the flue gases and by conduction through the tubes.
Consider- ation of the mechanisms of heat transfer in boilers will show that, while they are similar to those in surface condens- ers, some of the factors are not easily determined. For in- stapce, in most boilers the circulation of water is by nat- ural forces set up by the difference in density between steam and water, and as a consequence it is not easy to determine the velocity of the water passing over the boiler surface.
In a sinilar nanner to the effect of velocity on water film coefficients, the velocity of the flue gas over the surface of the tubes affects the gas film coefficient. Gaffvrt Fig. Boiler coot data. Example 19 shows the method of estimating the surface required for a water-tube boiler. Temp- erature of flue gas P, temperature of combustion air 80 P, temperature of combustion P, and temperature of fuel F. OD tubes spaced f in.
There will be 24 tubes per bank, and the tubes will be 12 ft long. Petermine the number of banks required, neglectiag the area of the sectional headers and the boiler drum. The furnace has plain brick walls. Acceptance was slow because of difficulties with water circulation, but a modern steam generator is almost all water-cooled furnace with only enough boiler sur- face to reduce the gas temperature to an economical point for use in econonizers or air heaters.
Reference to the illustrations of water-tube boilers wil2 show the application of furnace ccolirg. Heat transfer to furnace cooling surface is almost en- tirely by radiation and the heat transfer coefficients are extrem. The amount of radiant heating surface re- quired in a furnace is a function of several variables, such as the volume of the furnace, the temperature of the flue gas leaving the furnace, the sensible heat in the flue gas and the arrangement of the cooling surface.
Table XII gives some generally accepted data on values of heat release per unit of furnace volume. The temperature of the flue gas leaving the furnace should always be at least 2C0 P and preferably 25C F less tha the ash fusion temperature of the fuel used in order to avoid tightly adhering deposits in the convection sections of the steam generator. Arranfcmant of radiant heat transfer surface.
Figure VIII shows soir. Tetermine for the boiler of Example 1. The amount of effective radiant furnace coolirg surface required for a gas temperature of F entering the super — heater P less than the ash fusion temperature. Assume that the preheated air temperature is F. OD furnace tubes, spaced on three inch centers. The boiler screen consists of three bank's of 2i in. OD tubes spaced on nine inch centers. The plan dimensions of the furnace are 20 ft X 20 ft. VIII, Furnace cooling aurfacc daaign curvet. The total area i s : 14 Jissuming a slagging factor of 0.
The length of the furnace wall tubes will be approximately the same as the height of the furnace, or Assuming a slagging factor of 0. Furnace Refractories and I nsu I et i on-- In order to min- iirize heat losses fror furnaces, it is necessary to supply soire sort of insulating rraterial, and in order to prevent fire damage to insulation it is necessary to supply refrac- tory. Refractories are made from materials which have good resistance to damage from direct flame impingement.
They are usually supplied in brick form, although plastic refrac- tories are available. Figure VIII—15 shows some heat conductivity data for various refractory materials. Insulation is made of material which has good resistance to heat flow but which is not necessarily resistant to di- rect flame impingement. Several companies make insulating refractories which are very useful. Figure VIII shows some heat conductivity data for various insulating mater- ials.
Heat flows through the furnace wall by conduction and leaves the outer wall by radiation and convection. It is obvious that the heat lost from the wall surface must be equal to the heat flowing through the wall, so that the determination of the thickness of insulation required resolves itself into a trial and error process. Ordinarily it will be known ho? Determine the thickness of insulation required for a furnace wall which consists of Armstrong insulation sand- wiched between eight inches of hard burned red brick and nine inches of kaolin refractory brick.
The furnace temp- erature is P and ambient temperature is 95 P. Desir- able outside wall temperature is F. Temperature drops through the individual sections of the wall will be determined by trial. Recalculation of mean temperatures gives for red brick, 0. At these mean tempera- tures, k for red brick is 6. Then, for red brick. Thermal conductivity ot reffaotory materials. These mean temperatures are reasonably close to the previous calculations so that further trials are not considered necessary.
At this mean temper- ature, k for the insulation is 1. Better arrangements are water-cooled or air-cooled walls. In the water-cooled wall the inside. Thus, most of the heat passing through the refractory is salvaged and returned to the furnace. McMillan, L. Morse, F. New York, Orrok, G. Van Brunt, J. Superheaters are always made up of tubular elements and they are classified as to their arrangement in the boiler, that is, pendant or drainable, convection or radiant.
Pendant superheaiens are hung from headers which are located at the top of the boiler. This is the simplest arrangement, -but they are difficult to clean. Figure IX-1 shows a pendant superheater in a bent tube boiler. Pvndant suparhaatar in bant tuba boilar. Drainable super-- heaters are mounted in such a way that condensation in the elements can drain back to the headers. This type of super- heater is more diff- icult to place in the boiler because it requires that all of the element slope toward the headers, but they are easy to clean.
Figure IX-2 shows a drainable superheater in a straight tube boiler. Convection 'sup- erheaters are so named because they receive all or a ma- jor portion of their heat by convection from the flue gas. They have a rising temperature characteristic because of increase in heat trans- fer coefficients with increasing gas velocities. For this reason, modern boilers which contain convection superheaters alone have some means of bypassing part of the flue gas around part of t-he superheater to effect temperature control in the steam from the superheater.
They have a drooping temperature characteristic be- cause the temper- ature of the fire in the furnace remains essentially constant throughout the load range. Heat Transfer in Su perheater s--Heat transfer in a convection superheater involves a decreasing flue gas temp- erature and an increasing steam temperature. Wherever poss- ible the surfaces are arranged so that the gases enter the superheater at the same end at which the steam leaves.
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This counterflow principle results in more uniform temperature differences and higher steam outlet temperatures in compar- ison with parallel flow arrangements. Figure IX-6 shows a corojarison of the temperatures existing in the two arrange- ments. Example A. Determine the number and length of tubes required for a convection superheater for the boiler of Examples 17 and The tuoes are 2 in. Assume counterflow and a slagging factor of C.
Dis- pose of the superheater in two of the three boiler passes. Each tube has a flow area of rV4][2. Then the area for gas flow between the superheater tubes will be 53 - 1 4. Example B, The boile a combination temperature ri by the radiant the convection place part of tubes will be a length of B ant superheate r of Examples 17 and 20 is to be fitted with convection-radiant superheater. Half of the se in the superheated steam is to be supplied section which is in series with and follows section.
The radiant superheater is to re- the rear furnace wall cooling surface. One linear foot of 2. OD tube, in this particular wall arrangement, has an effective radiant surface of 0. Rehe ater S--A11 reheaters which are presently being built use flue gas as the heat source. For this reason, the reheater may be considered to be the same as a superheater. Figure IX-6 shows a modern reheating steam generator. Econom i zer s--An economizer is essentially a feed- water heater employing flue gas as the heat source.
Its primary purpose is to lower the temperature of the flue gas leaving the steam generator in order to increase the effic- iency. The overall hea t trans- f er coef f icient may be approximated f roni the same Babcock and Wilcox equation used for boilers. The tubes are 2 in. Tubes run lengthwise in the econoirizer casinff whose plan dimensions are 12 ft X 18 ft.
Gas inlet temperature is F, water inlet temperature is F and water outlet temperature F. They are of two general types: recuperative, either tubular or platej and regenerative. In he plate type the gas and air flow through alternate pass- ges. This type uses corrugated steel sheets for the heat storage material. Heat Transfer in Air Heater s--P[eat transfer in air heaters is a similar mechanism to those previously discussed. Example 24 Determine the number and length of tubes and number of passes on the air side required for a tubular air heater for the boiler of Examples 17 and The tubes are 1 in.
The gas flows through the tubes in a single pass and the air flows across the tubes. Plan dimensions of the air heater casing are 12 ft X 18 ft and the tubes run vertically.
The air inlet is 6 ft X 12 ft and placed so that counterflow is obtained. The air flow area per pass is 58 - 1 2. Each li in. OD tube has an area of 1. Each air pass is 6 feet high, so there would be 3 passes on the air side. For example, air heater su face is the cheapest, but combustion considerations limit ; temperatures to about 60C F for pulverized coal, oil or ga and to about F for stokers. It is usual to limit the water temperature leaving the economizer to about 5C F less than the saturation temperature in the boiler in order to avoid steaming in the economizer.
The temperature of the gas leaving the furnace is fixed by the characteristics of the fuel; the temperature of the water entering the economizer is fixed by the most efficient operation of the regenerative cycle; the temperatures of the gas and air leaving the air heater are fixed as previously mentioned; and the temperature of the air entering the air heater is fixed by ambient conditions. The boiler screen is ordinarily two or three rows deep and receives the major portion of its heat by radiation, so that it may be included as part of the furnace cooling surface.
Then, the temperature of the gas entering the superheater will be fixed as the temperature of the gas leaving the fur- nace, The temperature of the gas leaving the superheater will be determined by the necessities of heat transfer in the superheater. If the water cutlet temperature in a boiler-econo- mizer combination is not at least 50 F less than the saturation temperature in the boiler, try add- ing an air heater to the combination.
Table XIV gives some mass flows and heat transfer coeff- icients to be expected in commercial practice. After making an estimate from the table, the final values of economical temperatures can be arrived at by successive approximations. Assuming a boiler-economizer combination: The temperature of the water entering the economizer is greater than the temperature specified for the flue gas out- let temperature, therefore this combination would be im- possible. Parling, C. Drewry, M. But many more electric car models will hit showrooms in the next few years, and several factors have analysts convinced that is part of a major transition in the industry.
Don't see the graphic above? Click here. Government policies — particularly in Europe and China — are giving a boost to electric vehicles, as regulators consider not only the devastating impacts of climate change but also the value of improved air quality in cities. Auto companies around the world are gearing up for what will be a massive financial commitment.
Electric motors are simpler, making them easier to maintain and meaning they should last longer. Keeping them charged is cheaper than buying gas, an advantage that will become even more significant if gas prices rise. Plus, "they are fun to drive," says Tom Murphy, a managing editor at Wards Auto, which ranks the world's best engines.
On the other hand, gas-powered cars are cheaper to buy than electric vehicles.
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It's also quicker to fill up at the pump than it is to recharge, and the country is packed with gas stations, while charging station infrastructure is still in its infancy. But experts predict batteries will get cheaper, charging will get quicker, and chargers will become more readily available. Felipe Munoz, a global analyst at JATO, predicts electric vehicles will outsell conventional ones by Even people who love the internal combustion engine see the writing on the wall.
John Woods owns a Porsche On a recent Sunday, he joined other car enthusiasts at a parking lot in Alexandria, Va. The internal combustion engine is "the beginning of automotive engineering," Woods says. The rise of electric vehicles, however, doesn't automatically mean the end of the reign of the gas-powered car. Putting more battery-powered cars into circulation is only half of the equation.
The next question is, what happens to all the combustion vehicles already on the road? That's what environmental activists want, for the sake of curbing climate change. For instance, the Green New Deal proposed by Democrats calls for phasing out carbon-emitting vehicles within a decade — which would require not only very fast production of electric vehicles but also a sudden withdrawal of combustion vehicles from roads.
That's an ambitious target. But some version of that fast timeline could be triggered by very high gas prices or by bans or restrictions on internal combustion vehicles like some cities have discussed , at least hypothetically. Electric vehicles "are such better machines than the machines they're replacing," he says, that consumers might choose to retire their gas guzzlers long before the end of the vehicles' useful lives.
Others are far more skeptical of an accelerated timeline and anticipate the two types of vehicle will coexist on the road for a long time. Bill Visnic, editorial director at the Society of Automotive Engineers, is more blunt.