Bacalar ve baca hesabının bilgisayar programlanması

Abstract

Baca, esas olarak yanma ürünü gazları C duman veya atık gaz) taşıyan boru veya kanallara verilen isimdir. Ancak mutfak ve banyo gibi hacimlerin havalandırılmasında kullanılan boru ve kanallarada havalandırma bacası denilmektedir. Yapılarda kullanılan ve baca adı verilen bir başka eleman ise çöp bacalarıdır. Çöp bacaları çok katlı yapılarda çöplerin atılmasında ve bir merkezde toplanmasında kullanılır. Bu çalışmada duman bacaları üzerinde durulmuştur. Bacanın önemi vurgulanmış, bacalar ile ilgili tarif ve kelimeler, baca çeşitleri ve baca elemanları şekillerle açıklanmaya gayret edilmiştir. Bacaların sağlamaları gereken ana hususlar belirtilmiş, baca malzemelerinin uygun kullanma yerleri bir tablo ile verilmiş, baca kayıp ifadesi ve müsaade edilen baca kayıpları belirtilmiştir. ülkemiz sınırlı enerji kaynaklarını çok daha verimli tüketmek zorundadır. Bunun için uzun vadeli enerji tasarruf programına gerek vardır. Bu programda konut ısınması için harcanan enerjinin toplam enerji tüketimindeki payının % 41 olduğu ve konutlardaki kayıpların % 32 sinin bacadan olduğu düşünülürse, konunun özel ele alınması gerektiği ortaya çıkar. Yanmanın iyileştirilmesi ve verimin arttırılması için; baca kayıplarının ve baca gazı çıkışındaki dirençlerin azaltılması, baca gazı hacmini küçük olması gerekir. Bu sayede; yanma iyileşecek, verimi artacaktır. Yakıt tasarrufu sağlanacak, hava kirliliğinde azalma olacak, hem ülke, hemde aile ekonomisi kazanacaktır. Bu yüzden özellikle baca-kazan ilişkisi iyi incelenmelidir. Baca kesitleri, çeşitli Avrupalı firmaların hazırlamış olduğu diagramlar yardımıyla bulunur ve kontrol edilebilinir. Ancak burada her zaman kullanılabilen DİN 4705 KISIM l'e göre teorik baca hesabı ile birlikte bazı pratik bilgiler verilmiştir. Ayrıca yapılan bir bilgisayar programı ile, baca hesap süresi saatler mertebesinden, dakikalar mertebesine inmiş ve hata yapma ihtimali ortadan kalkmıştır

The purpose of a chimney is to emit a waste gas at a desired elevation. There are many emission sources of waste gasses: boilers, high temperatures processing, offensive fumes processes, etc. Gas travels from the emission source through a breeching to the chimney. A chimney is a major part of the plant or the building. It is a structure that also functions as a piece of equipment, like any other essential machinery for process or mechanical use. In the design of a chimney, we have to use chimney calculations which are given by DIN 4705 SECTION 1. By using these calculations, we will be able to calculate the pressures and the temperatures at different points of connecting pipes and chimneys. And we will also be able to calculate and control the cross section areas of chimneys and the connecting pipes. At the end of the calculations, there is a control part. In this part of the calculations, we have to control and conclude if the cross section areas of the chimneys and the connecting pipes and the height of the chimney and the length of the connecting pipes are available or not. After completing the calculations, we have to control the chimneys at five different steps whether the calculated chimney is available or not. These control steps are temperature control, pressure controls, velocity control, control of new calculated heat convection coefficient according to the ex-heat convection coefficient and the control of the maximum ratio of height over hydraulic diameter. The most important control steps are the first two steps. These are the temperature and the pressure controlling steps. We have to control the pressures whether the chimney is available to emit the waste gases- smoke - at a desired elevation or not. and we also have to control the smoke xii outlet temperature according to the dew point. The smoke outlet temperature through the chimney must be greater than the dew point of the fuel. If it is not, than the water vapour which is in the smoke will condens on the chimney surface. When this condensed water vapour come togather with SO in the waste gas, they will combine H S. And this will cause corrosion on the chimney surfaces. By the corrosion on the surfaces of the chimneys or connecting pipes, the smoke outlet resistance will increase and this will cause the emission of the waste gases and the combustion to go wrong. It will also damage the chimneys and the connecting pipes. The design of a chimney has a great importance. Because a chimney design has an influence on improving the combustion and increasing the efficiency of the combustion in the furnace. Small waste gas volume, low chimney loss and small outlet resistance of waste gas -smoke- from through the chimney. There are two variables in dry gas loss: stack temparature of the gas and weight of the gas leaving the unit. Stack temperatures varies with the degree of deposit on the heat absorbing surfaces throughout the unit, and it varies with the amount of excess combustion air. The effect of excess air is two fold: CI) it increases the gas weight, and C2) it raises the exit gas temperature. Both effects increase dry gas loss and there by reduce efficiency. A rough rule of thumb gives an approçimate 1 percent reduction in efficiency for about a 40 °F C22 C) increase in stack gas temperature on coal fired installations. High exit-gas temperatures and high draft losses with normal excess air indicate dirty heat absorbing surfaces and the need for soot blowing. High excess air normally increase exit gas temperatures and draft losses and indicates the need for an adjustment to the fuel/air ratio. The high excess air may, however, be caused by excessive casing leaks or by cooling air, sealing air, or aii - heater leaks. t -t. s ia Chimney Loss= ^rr c f CU2 t : The temperature of waste gases. C C) ;iii t. : The temperature of inlet air. C C) CO : The percentage of GO in the fuel. C%) f.-Average worth factor of the fuel family Combustion Efficiency= 100-CChimney Loss) To increase the efficiency, we have to reduce the chimney losses. To reduce the losses, we have to increase the temperature of inlet air or decrease the temperature of outlet waste gases. We must not forget that 32 percentage of the heat losses of the houses are the chimney losses. This also shows us the importance of chimneys. Cogeneration and heat reclamation are potentials for saving energy costs that are becoming feasible as the cost of energy rises. Cogeneration uses heat from the waste gas -smoke, exhaust air- to make hot water for industrial processes or to preheat the inlet air for combustion. Heat reclamation captures waste heat through heat exchangers for hot waters or space heating from the furnaces or engines. To decrease these losses, we have to use new energy conservation systems and recovery systems. For example, by the help of a cogeneration system, the inlet air can be preheated. By that way the temperature of the waste gas fc/111 also be reduced. As a result of this application, The chimney loss will decrease and the efficiency of combustion will increase. The advantages of increasing efficiency are the conservation of fuel, less fuel consumption, less fuel transportation costs, decrease in air pollution. Other design considerations are size, initial cost, material and life time cost. First design consideration is size of the bore (the smallest inside diameter, which is usually at the top of the chimney); next is height. Bore capacity depands on the type and volume of gas to be emmi ted and how the gas is fed to the chimney Ci.e., forced, induced, or natural draft). The right bore (internal diameter) helps maximize efficiency of the system, and minimize corrosion of the chimney interior. Size of bore affects flow of gas and can help keep temperatures hot enough Cor cool enough, depending on the xiv gas 5 to minimize corrosion. Flow to the chimney, as well as size of bore, determines how fast gas moves through the chimney. Flow is forced-draft, induced-draft, or natural draft. Forced- draft flow means that a fan at the emission source pushes gas through ductwork and breeching; induced-draft flow means that a fan in the ductwork, chimney, or breeching pulls gas from the emission source and pushes it through the chimney; natural-draft flow means that gravitational action of hot gas rising up the chimney pulls other gas from the emission force through the breeching. CIn forced- or induced-draft flow, specifications from the fan manufacturer and/or boiler manufacturer will help determine stack size. A recognized chimney designer can advise how much gas of agiven temperature moves per minute in a chimney of a given size and location by natural draft. ) Chimney height is the second design consideration. The taller the chimney, the more widely gas is disbursed and the better the natural draft characteristics. Local air pollution codesm, nature of the gas, surrounding structures, topography, and prevailing climatic conditions determine the desired height. In a natural-draft system the height also must be that which creates the desired draft A chimney designer actively involved in this work is the best source for determining the optimum bore and height, after considering the temperature and corrosive nature of gas from the emission source. A chimney must have structural integrity against windloading, climate, earthquake, fire, etc. Radial brick, reinforced concrete, steel, and more recently FRP are commonly used materials, singly or in combination. The chimney must also resist any destructive heat and chemical effects of the gas it handels; an interior lining is often mandatory to provide reasonable service life. for a corrosive gas of constantly low temperature with no chance of a boiler or process "runaway", lower-cost FRP is feasible. FRP also offers resistance against the destructive effects of acid-laden gas. The other most common destuctive effects are extreme heat, wide temperature fluctuations, and corrosive gas. A relatively new design is an independent insulated steel interior to a steel chimney. The assumption is that- for marginal operating temperatures- the insulating value of the dual walls will keep gases above due points. This mandates that flue gas temperature be kept hot enough at all times; otherwise interior steel will be corroded by acid attack. xv A chimney designer is also in the best position to recommend trade-offs between cost and optimum chimney size. Cost is a factor in chimney size, since tall chimneys cost more per food than shorter chimneys of the same construction material. Chimneys with small bores cost absolutly less, but proportinately more than those with large bores. Other recommendations might change how the gas enters the breeching (with stronger fans, different flue temperatures, etc.) to allow less expensive construction to perform well. Chimneys deteriorate with age due to weathering as well as through normal usage under original design considerations also operating conditions and hence the nature of the emmi ted gas, may change over the years. Many common changes produce gases at more corrosive, or lower the dew point of already corrosive gases (causing condensation on the interior wall that the chimney's original interior can not handle). Exampels of changes that invite corrosion are use of new fuels, boiler conversion, elimination of incineration, scrubber installation, cyclone installation, use of economizers and other energy-saving devices, use of other pollution-reducing devices and capacity adjustments. A chimney design firm can analyze an existing structure in terms of current operating conditions and easily advise if there is a potential corrosion problem. Using a computer program which was studied in this case, calculation, design and control periods of a chimney decreased from 2-3 hours to 5-10 minutes. And the probabilty of making mistakes is also prohibited.