Alev duman borulu buhar kazanlarının dizaynı için paket program

Abstract

Bu çalışma, buhar kazanlarının ısıl, yük kaybı ve mukavemet hesaplarını yapan ve sonuçta ortaya çıkan kazanın teknik resmini Autocad ortamında çizen bir paket programın hazırlanmasını konu almaktadır. Giriş bölümünde kısaca buhar kazanlarının tanımı verilmiş, kazan seçiminde nasıl bir yol izleneceği açıklanmaya çalışılmıştır. İkinci bölümde alev duman borulu kazanlar hakkında bilgi verilmiş ve bu kazanların üstünlükleri ve dezavantajları anlatılmıştır. Programın tanıtılması üçüncü bölümde yapılmıştır. Hesapları yapılan kazan tipleri, yakacağın nasıl seçileceği, temel alınan hesaplama yöntemleri açıklanmıştır. Alev geri dönüşlü kazanın yapısı ve hesap şekli iskoç ve kalorifer kazanlarından farklı olduğundan hesap şekli ayrıca verilmiştir. Hesaplamalarda sıkça kullanılan yakacak, su buharı, antalpi, iletim, taşınım ve yük kayıplarına ait tabloların nasıl programın kullanabileceği hale getirileceği, tabloların veri şeklinde bilgisayara girilmesi grafiklerle açıklanmıştır. Yine bu bölümde, hesaplamalar sonucunda ortaya çıkan kazan verilerini okuyarak çizimi gerçekleştiren Autolisp programı hakkında kısaca bilgi verilmiş ve hem Autolisp hem de programın akışı anlatılmıştır. Ayrıca her iki programın akış şemaları da bu bölümde verilmiştir. Programın uygulama örneklerinin verildiği dördüncü bölümde, üç tip kazanın değişik yakacaklar kullanılarak hesapları yapılmıştır. Doğalgazlı, sıvı yakıtlı iskoç, alev geri dönüşlü ve kalorifer kazanlarının konstrüktif verileri gösterilmiştir. Sonuç bölümünde programın getirmiş olduğu kolaylıklara ve üstünlüklere değinilmiştir. Ek kısmında ise program listesi verilmiştir.

This program consist of calculation of fire tube boilers and drawing of the boiler on the Autocad make use of the data belong to the calculated boiler. Chapter one contains introduction of the boilers and choice of the convenient boiler to meet varying requirements as to initial cost and fixed charges. Fire tube boilers are outlined and classified in chapter two. Advantages and disadvantages and illustration of some design values of these, which are heating boilers, scotch boilers, fire-returned boilers, are also given in this section. Introduction of the program begins in chapter three. Program is carried out in two main parts. The first part which is written using TC++ is about calculation of boilers and the second part is the drawing of the calculated boiler and it is written by using Autolisp. These two parts completely different from each other except a common point. The second part of the program written in lisp utilizes the data which is calculated by the first part, in order to draw the boiler. The program written in C++ can design scotch boiler, heating boiler and fire-returned boiler. Furthermore superheater and economizor choices are available in scotch boiler. User can choose both or one of them or none. Calculation way of the heating boiler and scotch boiler are similar but fire-returned boiler has a different calculation way. Therefore a special subprogram was written for it. XI When doing the boiler calculation, tables and figures are often used. Therefore, these should be entered as a file so that program can read the data to use in calculations. The common point of the graphs used in calculatons is that a value is read with respect to given two known values from the figure. If one calls the known values as x, z and unknown value as y, to find the y value, x and z are used. To do this, extra x and z values are needed. Then the x and z values are compared with extras and determine the range in. Therefore, especially at the bending point of the graph more values should be given in order to reach precise value. Next, using enterpolation unknown y value is obtained. In order to perform all this step, a subprogram is used by the main program. Subprogram reads the data related to the graph and compared with the given values. Then, it sends the determined value to the main program and main uses this in calculations. All the data belong to the graph needed are saved as "name".dat to be read easily. Calculations belong to the temperatures and losses are made for thes* parts of boiler below. 1. Furnace 2. Corrugated tube 3. Fire box 4. Smoke tubes 5. Reversing chamber 6. Superheater 7. Ekonomizor At the furnace, in order to calculate the temperature ones need to know theoretical smoke enthalpy, saturated water temperature, emission coefficient, surface area that emits radiation and surface area that absorbs radiation. To calculate the theoretical smoke enthalpy, fuel consumption, excess air coefficient, flow rate of air, air enthalpy and flow rate of smoke are used. Calculation is based on a prediction. First, temperature is predicted and assuming this temperature correct, calculations are made. At the end of the calculations calculated enthalpy and enthalpy belongs to the predicted temperature compared with each other and if difference is not acceptable a new temperature is predicted and calculations are repeated until the difference is small enough. At corrugated tube, fire box and smoke tubes, calculations are based on prediction same as the furnace. Having predicted a temperature, enthalpy difference between inlet and outlet of the part is calculated. Since the inlet enthalpy is known, outlet enthalpy is xu obtained easily by substracting enthalpy difference from inlet enthalpy. Then, obtained enthalpy is compared with enthalpy belongs to the predicted temperature and if difference is acceptable temperature is assumed correct. If not calculations are repeated. In order to calculate the enthalpy difference, overall heat transfer coefficient, which is sum of the radiation and convection heat transfer coefficients, logarithmic mean temperature difference, heat transfer area and flow rate of the smoke should be known. Some of these variables are calculated by using predicted temperature. If prediction is not correct enough, all these variables must be calculated again. At reversing chambers, 10 or 15 °C temperature decrease is assumed instead of doing calculations. Superheater is a simple heat-exchanger. Saturated steam goes into the superheater and it is heated by the smoke to be superheated steam. Basicly, using heat equilibrium at superheater, the equation can be written like below. Vg-Ogm - igout) = mb. (ii - i2 ) (1) Vg is flow rate, igm is inlet and igout is outlet enthalpy of the smoke, mb is flow rate of the steam, ii and İ2 are enthalpy of superheated and saturated steam respectively. From this equation, igout is calculated easily and temperature is obtained using this. Economizor is also a heat-exchanger and it heats the feed water by means of the smoke. Equation that is used for the superheater can also be used for economizor. Here Vg, igi", igout are belong to the smoke and mb, iı, İ2 are belong to the feed water, ii, outlet enthalpy of feed water, is obtained from the equation and temperature is found. Two kind of losses are available in boilers. These are minor losses and major losses. Losses at valves, bends, tees, etc. are called minor losses. Major losses are the friction losses in the tubes. Friction losses can be calculated by multiplying length and friction loss coefficient. Friction loss coefficient depends on smoke velocity, mean temperature of smoke and tube diameter. Minor losses are directly proportional to density, minor loss coefficient and velocity squared. Minor loss coefficient varies at different conditions such as exit loss, entrance loss, sudden expansion, sudden contraction and bending. These values can be read from tables. XUl There are friction loss and exit loss in corrugated tube. Since, the friction loss at the corrugated tube is very little, it may not be taken into account. Overall loss is sum of the friction and exit loss. At the fire box, friction losses may be neglected. It is enough to calculate the minor loss due to the 180° bending of the smoke. At reversing chambers also just losses that occurs due to the bendings of the smoke are calculated. At the tubes, both friction loss and minor losses should be calculated. Here, minor losses are sum of the sudden expansion and sudden contraction. Friction loss and other losses are calculated like explained at the top. At superheater and economizor, special equations are used so as to calculate the losses. These equations depend on the velocity and temperature of the smoke, number and diameter of tubes and distance between tubes. When the program runs, a main menu comes to the screen. First, type of the boiler is choosen. After the choice user is supposed to enter the general data belong to the boiler which is choosen. Then, main menu comes back and type of fuel is choosen. Fuels that can be choosen are natural gas, heavy oil and diesel fuel. After choosing the fuel, program displays the lower heating value of the fuel. Then user is supposed to enter excess air coefficient and furnace consistency. Next, furnace diameter is asked the user and according to this furnace length and temperature are calculated. Then, at the end of the furnace, temperature, enthalpy, mean temperature, logarithmic mean temperature difference, CO2 and H20 radiation, convection and radiation coefficient are calculated in sequence. If calculation is about fire-returned boiler, smoke tube calculation follows the furnace. In this section, number of tubes, diameter of tubes and turbulator availability are asked the user. Then, general data mentioned at the furnace are displayed. Next, front and back temperature decrease at reversing chamber taking into account, strength calculations are started. XIV If boiler is a scotch boiler or heating boiler, user is supposed to enter fire box diameter. According to this, general data are displayed. At the smoke tubes section, tubes are inserted depending on its diameter, numbers and fire box diameter. If the program could not insert the tubes user is supposed to decrease the number or diameter of the tubes. After finding the ideal solution next step is performed. Furthermore, if superheater or economizor are available, calculations are made for them. Next step is calculation of losses. Losses at main parts of the boiler are calculated in this section. Sum of these losses give the overall losses and chimney calculations are made by using this. After the loss calculation strength calculation starts. Two types of standart steel are available in the program. User can choose one of them and program uses the spesifications of this steel such as tensile strength. Main parts which are calculated by the program are like below. 1. Boiler body... 2. Dished ends 3. Furnace 4. Stay bolts At the boiler body, utilizing pressure, boiler body diameter and tensile strength of the chosen steel, plate thickness is obtained easily. For dished ends, pressure and maximum allowable circle diameter at section which has not stay, are adequate to calculate the sheet thickness. The sheet thickness of furnace is calculated by using diameter and pressure. To calculate the stay bolts diameter, pressure and distance between stay bolts are used. Having finished the strength calculation general data are obtained to draw a sketch and front view and side view are plotted. If the user does not satisfy the design and data, can return to the start of the calculation. User also can return to initial calculation at furnace, fire box, tubes, superheater, economizor, losses and strength calculation. Before the program finished, general data are written in a file to be read by the drawing program and displayed on the screen. Then, main menu comes back and user can exit or starts a new calculation. Second part of the program is a simple Autolisp program allows the user can use the Autocad more efficiently. Autolisp is a kind of lisp, which can use the Autocad commands. Lisp is a programming XV language that is used at artificial intelligence works. Lisp means List Processing. The program written in Autolisp, first of all decides the which boiler is plotted utilizing the file created by the first program and read the data from the file. Then, it assigns the data to variables. AO paper is used for drawing but user can change the paper size using Autocad commands easily. Different colors are used for different parts of boiler in the drawing. Using the Autocad commands like circle, line, polygon, boiler is plotted. After that, user can change the drawing easily according to needs.