Combustion Engineering Software Provides a Practical Tool for Solving Combustion and Heat Transfer Problems
The complete package includes a References program devoted to common combustion-related references; an Applications program for guidance through the design of combustion and furnace systems; a System Design program that steps the user through the process of designing an entire combustion system including all pipe sizing for air, gas and oil lines; a Keyword search to lead the user directly to a specific program; and a Glossary of terms for short definitions and explanations of factors and variables used in the combustion engineering program. The subroutines within each program contain excellent Help menus describing the subroutine's function, options, limitations, required input, subroutine output, and operating instructions.
PROGRAM CAPABILITIESThe e-Solutions package is not an educational primer on combustion fundamentals. It is a simple-to-use tool containing 22 practical scientific routines to be used by experienced combustion engineers who are responsible for designing, maintaining and improving fuel-fired furnace systems. The program incorporates many of the concepts found in textbooks and handbooks into a single package so the need to reference such printed materials is minimized or eliminated. All calculations are carried out through rigorous scientific analysis rather than using rules of thumb, yet no theories of combustion or associated equations are found in the foreground of the program.
The Reference program may be used to find general technical information relating to thermal processing systems design. The program is comprised of several subroutines that provide tabulated physical property data on 22 gases and liquids including custom mixes at temperatures and pressures, 20 fuels including custom mixes, and physical properties of 21 different metals including data on emissivity, thermal expansion, melting point, and conductivity (Fig. 2). Other subroutines allow the user to easily calculate unit conversions, Wobbe index, fuel comparisons and energy savings, combustion products and available heat, branch piping design, and flow parameters based on principles of fluid mechanics. The Applications program includes a series of software tools that can be used for building combustion systems. These include calculations for sound, flue sizing, furnace heat losses, radiation heat transfer, forced convection heat transfer, natural convection heat transfer and emission calculators. The user is requested to simply enter the appropriate technical information needed to make the specific calculation and the answers are returned immediately at the click of a button.
The System Design portion of the package allows the user to build an entire combustion system and generate a bill of materials. The program encompasses five input steps for fuel selection and furnace specification (including inputs for single-zone or multi-zone furnaces), burner selection, air line component selection, blower selection, fuel line specification (including light and heavy fuel oil systems) and component selection. Outputs include air piping and component selection with their associated pressure losses, system air requirements and blower performance parameters, a complete list of air line and fuel line components for each zone of the furnace. Also included in this subroutine is an interpretation of the 1999 NFPA 86 safety valve requirements for reference to combustion systems design specifications.
SELECTED PROGRAM SUBROUTINESReference/Properties of Solids, Liquids and Gases
As previously mentioned, this subroutine supplies the user with a reference "library" of materials properties pertaining to combustion and heat transfer. Properties can be obtained by simply selecting the appropriate material from the "Properties" window. For gases and liquids, the user selects the fluid (or may input the composition of a custom mixture) and the conditions of temperature and pressure. The subroutine returns the density, specific gravity, specific heat, absolute and kinematic viscosities, enthalpy, ratio or specific heats, conductivity, and Prandtl number. For solids, the user simply selects the materials from a materials table and inputs the temperature of concern. The subroutine then returns the melting point, boiling point, heat of fusion, density, specific heat, conductivity, and emissivity.
This subroutine is exceptionally easy to use and provides instantaneous conversion values for a multitude of engineering parameters. The user simply selects the appropriate conversion "from" units and "to" units and enters the value they wish to convert into the "from" units data input line. The converted value is displayed immediately in the "to" units data output line (Fig. 3).
This subroutine calculates the pressure drop through a user-designed piping branch based on fluid temperature, the fluid's inlet or outlet pressure, the branch components and the fluid flow rate through the branch. The required input parameters include the fluid being considered, fluid temperature, fluid inlet or outlet pressure, a selection of branch components, and the fluid flow rate.
The subroutine output consists of a table listing the part name, part size, component flow coefficient (Cv), component equivalent length, component inlet pressure, and pressure drop through each component. In addition a "branch summary" is provided that includes inlet and outlet pressures of the designed branch, the fluid flow rate, the branch equivalent length, the branch Cv, and the total pressure loss through the branch (Fig. 4).
The fuel combustion subroutine calculates combustion products and a variety of outputs based on a selected fuel and the specified combustion conditions. The inputs include the fuel type percentage of excess air; air, fuel and exhaust temperatures; and fuel flow rate. Other input options include temperature and percentage of the recirculated flue gas, and the purity of oxygen as a percentage of the air/oxygen mixture.
The subroutine output includes composition and specific gravity of the fuel, gross and net heat content, theoretical air/fuel ratio, percent by volume of combustion products, available heat, air flow rate, actual flue gas flow rate, adiabatic flame temperature, and several other outputs relating to flue gas exhaust.
This subroutine is very useful in determining the energy savings that result from two different combustion conditions and the difference between the use of electricity compared to combustion (Fig. 5). Combustion conditions may be entered for two cases based on the fuel selected. Input data includes percent excess air, combustion air temperature, percent oxygen in the combustion air, percent flue gas recirculation, flue gas temperature, exhaust temperature, and fuel preheat temperature. The subroutine will output the available heat in percentage for both cases and the percentage energy savings of one case over the other. The subroutine can also calculate fuel costs.
Applications/Forced Convection or Radiation Heat Transfer
Heat transfer characteristics may be calculated through either forced convection, radiation, or natural convection subroutines. The forced convection subroutine calculates the heat transfer coefficient and heat flux for selected fluids and geometries at a specified fluid temperature and wall temperature. After selecting the fluid type, geometry, fluid temperature and pressure and flow rate, the program outputs the Reynolds number, Prandtl number, Nusselt number, heat transfer coefficient and heat flux.
The radiant heat transfer subroutine allows the user to calculate either view factor or radiation heat flux for selected geometric cases. For the view factor calculation, the user selects the geometric configuration (which is then displayed schematically on the screen) and inputs the critical dimensions. For the heat flux calculation, the user selects the appropriate geometric case and dimensions, the refractory lining and load materials, input wall temperature, load temperature and radiating gas temperatures. The resulting heat flux or view factor is then displayed as output. A typical radiant tube application is included with inputs for furnace gas composition.
This subroutine calculates the flue size for a desired furnace pressure or calculates the furnace pressure for known flue sizes. The program can also be used to size air jet flue dampers for a desired furnace pressure when the flue size is known. Here, the user enters fuel type, flue shape, flue dimensions, exhaust temperature, firing rate, and excess air (among other variables), and the program returns values for bouyancy pressure due to stack height, pressure head loss at the flue passage entrance, maximum stack flow, furnace control point pressure or flue size, and other variables depending on the program option selected. An air damper option provides additional output for air jet angle, hole size, air manifold pressure and flow rate, and the number of holes in the air jet manifold.
Another practical subroutine included in the package is the furnace heat loss calculator (Fig. 6). While the routine is not a refractory design program, it does provide generic refractory data for use in estimating heat storage and heat loss for the sizing of the combustion system. The routine contains six (6) refractory types from which to choose and there is an option for either one or two layers of refractory. The refractory types include high density fireclay brick, insulating firebrick, lightweight castable, low cement heavy castable, castable insulation, and ceramic fiber.
Heat loss through furnace openings is handled by one calculation, which needs to be dimensioned to represent the entire area of openings in the furnace. The dimension of the width must be fairly accurate since this dimension effects the view factor in the radiation loss calculation.
For this subroutine, the user enters information on furnace shape, furnace dimensions, furnace temperature, furnace construction materials, wall, roof, and floor thickness, and floor material. The program is limited to rectangular or cylindrical shaped furnaces and one or two layers of selected wall material. The subroutine then calculates heat fluxes, heat storage, heat losses, and interface temperatures for the top, side walls, and bottom.
The combustion system design program offers the user an excellent opportunity to review and control the combustion equipment selection process. The six-step program requires the user to enter furnace parameters, general burner specifications and heat requirements, air line specifications and components, blower requirements, and fuel line specifications and components. This complete program allows the user to understand the system design stage and provides a components list (with model numbers) along with other various system specifications and performance output data (Fig. 7).
Another practical feature of the program is the presence of the NFPA 86 safety value requirements (as interpreted by Hauck Manufacturing after review by the NFPA). This feature provides guidance for furnace/combustion system design engineers with respect to regulations that govern the design of these systems.
SUMMARYThe e-Solutions software toolkit provides combustion engineers with a quick and easy method for finding answers to many combustion-related problems and questions. The software package can be used during the early stages of a combustion system design project, as well as to optimize an existing operational system. Information on materials, fuels, emissions, heat transfer, sizing and system efficiency are readily available in a "point-and-click" package.
In addition to specific reference programs and design applications, the system design package is an excellent program for designing a complete combustion system. The user is guided through the design process in a step-by-step manner and can gain a more thorough understanding of how a combustion system is assembled. Incorporating the other reference and application subroutines will provide the end-user with an excellent overview of the capabilities of their combustion system. IH