Vent Lab. #9 & 10 Computer Simulation

Transcription

1 Vent Lab. #9 & 10 April 14, Introduction Network analysis of mine ventilation systems dates back to 1854 when Atkinson solved a small network problem using a method of succession approximation. This method of network analysis was later adapted and developed by Cross in 1936, then modified by others for solving ventilation network problems. There are many ventilation simulation programs available on the market, and most of which offer similar features in terms of data input, output, fan performance data, etc. (Check website for details). The simulation program used in our lab is VnetPC for Windows by Mine Ventilation Service, Inc., Fresno, CA.. 2. Network Simulation Using VNETPC 3.1 for Windows VNETPC is a micro-computer software package designed specifically to assist in the design, planning and control of underground ventilation systems. Using data from ventilation surveys or determined from known airway dimensions and characteristics, existing ventilation network can be simulated in such a manner that airflow rates, frictional pressure drops and fan operating points approximate those of the actual system. Following acceptable correlation with the existing ventilation system, network exercises may be conducted to determine the system requirements for future mine developments or economic evaluations to improve the efficiency of the current system. A. Hardware Requirement VnetPC for Windows was designed to operate on any IBM compatible micro-computer running Processor. A minimum of 4 MB of RAM memory, 1 MB hard disk space and a VGA display are needed. For VnetPC, it requires a Microsoft Windows 3.* or Microsoft Windows 95 operating system is needed. The package was developed for the Windows 3.* operating system, but will run successfully using the Window 95 operating system. B. Capabilities and Features All ventilation simulation programs today are based on the Kirchhoff Laws: The algebraic sum of the volume flow rates entering and leaving each junction totals zero. The algebraic sum of the frictional pressure drops along any closed circuit totals zero. The code then utilizes an accelerated form of the Hardy Cross iterative technique to converge a solution. In short, the iterative procedure is as follows: The code evaluate the network and constructs a number of meshes; the minimum number being equivalent to the number of branches minus the number of junctions plus one. Each branch in the network is represented in at least one closed mesh, and each mesh contains no more than one high resistance branch. 1

2 For every mesh, a flow quantity correction factor is calculated using airway resistance, fan characteristic curves and initial estimates of airflow chosen by the computer. The quantity correction factor is applied to the estimated flows of all the branches in the mesh. This is performed for each mesh in the network. This process is repeated iteratively until Kirchhoff's Second law holds to a prescribed accuracy for every mesh in the network. The resulting network is then balanced. C. Capabilities and Features VnetPC is structured as follows: Execute Ventilation Simulation Manage Network Files EXECUTIVE MENU Exit Set Operating Environment View or Print Output Plot Results Gas Distribution Analysis Some of the important features are listed as follows: Network size This package is capable of analyzing networks of up to 1,500 branches and 200 fans. Files larger than these limits may encounter problems. Operating units - The package can process data in either Imperial or System Internationale units. Flexible output format The output is separated into four parts: (1) Fan operating points, the power requirements and operating costs, based on power charges supplied by the user. (2) Frictional pressure, drop, airflow rate, resistance, airpower loss and cost of ventilating is listed for every branch. (3) If fixed airflow quantities are utilized, a regulator resistance or booster fan requirement is listed separately. (4) At user discretion, a pressure reference table may be printed which lists the relative pressure at every junction in the network. This is useful in determining the direction of leakage trends. 2

3 Complete data file management - User data files for input and plotting purposes can be listed, modified, printed, saved under any name, saved on any drive, or deleted. See separate Operating Manual handout for further details. 3. Assignment Problem The sample problem is a three-unit coal mine located in Illinois (see attached schematic for details): 1. Intake airshaft: 550' deep, 12' diameter (11' finished with k = 25); Return airshaft: same as intake except for the exhaust fan on top of the shaft. 2. Main entries 2 intakes; 3 returns 3. Panel entries 2 intakes; 2 returns 4. Operating units requires 25,000 cfm/unit 5. Fan curves (see separate file) 6. You are to simulate belt and track as neutral airways. Assign one leakage airway for every 500' between intake and neutral, and neutral to return, and at all intersections. Since leakage airways are airways with exceedingly high resistance, use R = 200 for the furthermost point (from portal) and decrease this amount by 20 for every 500-ft toward the portal. In case there are two R values developed for the same point (for example, the intersection of Unit-2 and Unit-3), use the higher value. 7. Because of diesel equipment used underground, a minimum of 10,000 cfm should be provided in the track entry in order to be in compliance with the MSHA regulation. 8. Mine airway resistance/1,000' Intake Airways: 3 entries entries entry Return Airways: 3 entries entries entry Neutral Airways: Main entries Submain entries

4 Panel entries For this lab, a team of three, or a total of eight lab reports are expected. You lab report should include: 1. A hard copy of the output, with appropriate interpretations of results (fan pressure, total air quantity circulated, booster fan needed, if any, etc.) - the kind of information you would like to see if you were the superintendent. 2. Make sure there will be at least 25,000 cfm reaching each unit; no airflow reversal (no negative airflow) in major airways; leakage airways are located at least every 500 feet and at all intersections (different fan curve may be necessary if the above conditions are not being achieved), etc. In a 30-minute presentation, each team is to present your final findings of this project at the end of April or beginning of May. This is a team effort so all members are expected to participate in the presentation. I hope to locate a common period where the presentation can be conducted in front of the entire class. 5. Procedures for Running Ventilation Program Eight full versions of VnetPC for Windows have been installed on eight machines in Mining Computer Lab (Room 130 McNutt). The following are the step-by-step procedures for using the program. 1. Access VNETPC for Windows (There will be three icons: VNETPC for Windows, Fan File Manager, and User Information), select VNETPC for Windows icon and hit RETURN. 2. Create a new file under FILE; 3. Under Model Information, select Edit Data, hit RETURN; 4. Under Edit Model Data, type the following (information in bold are input and explanations are in italics): Description: Title: Min-218 Comment1: Lab 8-10 a. Title simply generates file name b. Comment1 provides comments relevant to that particular run; you can input other comments you want to input for example, your company name, your boss' name, etc. General Data: Ave Fan Efficiency: 80% Units: British Cost of Power: 6 cents/kwh Reference Junction: 1 4

5 a. Average Fan Efficiency is used to calculate brake horsepower from air horsepower; b. Cost of Power is used to calculate cost of energy for that particular branch or for the entire system; c. Reference Junction is preselected to be 1, although you can change to other numbers if necessary. 5. Access Branch Input under View menu: To input branch data, select Add Branch under Edit menu; Hold down Shift + Enter to prompt a space for inputting the next branch; There are four types of input format: Type 1 R fixed airway resistance. This value may be calculated from survey data or determined from airway dimensions and friction factor. Type 2 P & Q pressure drop and air quantity. These values can be entered as obtained from a pressure survey. Type 3 K, L, L eq, A, Per airway physical characteristics (friction factor, length, equivalent length of shock loss, perimeter and area) used to calculate resistance. Type 4 R/L, L, L eq resistance per unit length, airway length and equivalent length. This option allows direct calculation of resistance from previously measured or calculated typical air resistance. A 5th type, the fixed quantity airway, is accessed through menu or Toolbar. (No consistency of input format is required, and data entries are prompted for each individual branch.) 6. After all branches have been entered, input fan information: First, select airways where fan(s) is (are) located; Choose Fan under Edit menu to prompt Fan Data dialog box; Enter 5.5 in the Pressure box; (this is the fan pressure required for the VNetPc to use internally; the closer your final fan pressure is, the less time it takes to compute); Select Edit Curve... to prompt Fan Curve dialog box; type in the following information: Fan Name: Joy MXXXX Fan Setting: XX - whatever you end up using Comments: (optional) Fan Curve Points:... (Use Add Point... to add all 10 points to the curve and use Edit Point... for any corrections) Select Execute Simulation under Tools menu; select View Errors under Tools menu for correction; Select Print All under File to print output; only print the portion(s). 7. Go back to original data for running other scenarios. 5

6 Submain 1,500' Panel 2,000' U-2 U-3 Panel Ventilation Schematic (Not to Scale) 4,000' 2,000' Main Intake Airshaft 2,500' Panel U-1 Mine Fan Portal 6

7 Attachment Network Simulation and Simulation Packages 1. Introduction Network analysis of mine ventilation systems dates back to 1854 when Atkinson solved a small network problem using a method of succession approximation. This method of network analysis was later adapted and developed by Cross in 1936, then modified by others for solving ventilation network problems. The use of computers to simulate a mine ventilation system dates to the early days of the electrical analogue. The electrical analogue was a large set-up consisting of several resistors, rheostats, voltage sources and radio valves and was used to simulate the performance of a ventilation network. The analogue method was reportedly used by Pavlovsky in 1918 to study the seepage of water. Its first use in mining was apparently reported in Germany in 1952, and in 1954 in the United States. One of the earliest digital computer programs for simulating mine ventilation networks was written by Dr. R. E. Greuer of West Germany in the late 1950s which was later converted to the so called Michigan Tech Program, then, the Bureau of Mines version in the late 1970s. In the U.S., Dr. Y. J. Wang wrote the first version in the late 1960s and later became the popular Penn State Mine Simulator. Dr. M. McPherson of the United Kingdom wrote his simulation program in the mid to late 1960s. Programs have also been developed in, Japan, U.S.S.R., France, and South Africa, and by 1970 several models became available. Papers in this area include those by Hartman and Trafton, 1963; Wang and Hartman 1967; Wang and Saperstein, 1970; Stefanko and Ramani, 1972, 1973; Barnes, 1975; McPherson 1974, 1976; and Hall, Unsted and Lintott, 1976, and Tien in Currently, there are well established models for ventilation network simulation, as well as for the study of other parameters in mine ventilation. They enable the ventilation engineers to simulate several system alternatives and select the most efficient and cost effective ventilation system desired. All these programs were based on Hardy Cross iteration method, which is basically a series of successive approximations based upon two Kirchhoff's laws for electrical circuits and that the Atkinson's Equation. These laws state that continuity of flow must hold at junctions (conservation of mass), that total change in pressure in a closed circuit must be zero (continuity of potential), and that airflow follows the relationship of head loss equals resistance times that quantity squared, H = RQ 2, Atkinson's law). Recent development in micro- and mini-computers have further facilitated input/output, user interaction, and user-friendliness. They have enabled ventilation engineers to further extend their application into evaluation of underground refrigeration, environmental simulation, and others. Ventilation problems that can be solved by the computer program include: solving complex ventilation systems with many entries, shafts, fans, and working faces; fan selection determining optimal fan settings for efficient operation; determining the amount of regulation required to control airflow; determining the effect of air leakages on the overall system selecting optimal fan locations 7

8 determining possible effects of improvements to airways such as cleaning rock falls, smoothing airways, and other means of decreasing airway resistance. Progress in development of hardware and software will continue apace. There will be further improvements in the computing abilities (speed and memory capacity) of personal computers. The power of today's super-computers will be available in the office machines of tomorrow. How? One of the most significant recent advances has been the advent of the parallel processor computer. The current generation of machines utilizes a single microchip processor through which passes all of the calculations in sequence, binary data being transferred from and to memory as directed by the program. Even with the enhanced speed of modern computer chips, the single processor has become a bottleneck. Current computer simulation programs were written for the single processor which has to calculate each network sequentially. The computing time for one iteration of the complete network is the time taken for every mesh (a closed loop formed by several airways in the network) to pass through the processor, one after the other. The corresponding time on a parallel processor will be reduced to that required for one iteration on the largest mesh only. For example, on current personal computers, a 500-branch (airway) network may typically take several minutes to analyze. On a parallel processor this will be reduced to a few seconds. The next generation of network programs will provide powerful optimization features. In addition to giving distributions of airflow, pressure drops and airpower losses, etc., such programs will give direct advice on the duties and locations of fans and regulators, and the recommended sizes of proposed new arterial airways. Embryo but practical versions of this type of application for selecting the optimum combination of fans and regulators are already at the testing stage. While ventilation network analysis programs, and variations on them, have dominated software development and application, other programs continue to be produced. These will, increasingly, enable ventilation engineers to conduct sophisticated analysis including shaft design, gas drainage system analysis and air conditioning configurations. All these will help us work toward the ultimate goal ventilation automation. 2. Existing Ventilation Simulation Software Most of the ventilation programs currently available provide an interactive, understandable interface with the user. They can categorized into two major groups: mainframe ventilation programs and microcomputer ventilation programs. 1) Michigan Tech. Ventilation Program This program is derived from early versions of programs developed in West Germany in the 1960s. The program, using Hardy Cross iterative technique to balance the network, is also very similar to the program of the British National Coal Board which was issued in Modifications made include identifications of airways, calculations of natural ventilation pressure, efficient fan curve approximations, streamlined output. 2) MFIRE 1.29 Bureau of Mines This program is derived from early versions of programs developed in Michigan Technological University. It is currently in the microcomputer version and, like its predecessor, is capable of simulating routine mine ventilation network problems and also models the response of ventilation network under the influence of thermal disturbances such as mine fires (both fuel rich and oxygen rich type) and cooling stations. Fires can be specified as a fixed source of output heat and products of combustion, or allowed to vary as a function of oxygen delivery. In addition, the program calculates the concentration, distribution, and propagation of contaminants in a ventilation system, such as fumes of a fire. Unlike previous network programs, MFIRE ac- 8

9 commodates both steady and transient disturbances, including unplanned events such as fires as well as routine events such as fans starting and stopping or doors opening and closing. The program has extremely flexible input requirements and output options. Natural ventilation, recirculation, and positive and negative thermal and mechanical energy inputs to the ventilation system are accommodated. Mass-based flow rates are utilized with reference to a known temperature and air density at a specified location. Methane evolution can also be specified. 3) Mine Ventilation Services, VNETPC 3.1, CLIMSIM. This is an interactive network analysis program with graphic output provided for a pen plotters, but not on the CRT screen. Four methods of entering or calculating resistance are provided. VNETPC is a similar program for large networks which runs on a mainframe computer. The CLIMSIM program simulates variation in psychrometric conditions along any mine airway, shaft or slope that affect climatic conditions in mines. Data requirements include airflow and wet bulb/dry bulb temperatures at inlet, airway geometry and age, rock thermal properties, and power and positions of equipment and cooling plant. Other programs available from Mine Ventilation Services include: NETCOR, correlation between measured airflow and computed airflow. PSYCHRO, psychrometric table or chart replacement. GASSIM, gas emissions and concentrations. BARSUR, thermodynamic relationships for pressure drops, airway resistance and natural ventilating pressures. LEAKAGE, air leakage through a line of stoppings/doors between intake and return airways. Other programs include calculations of rock thermal properties, flow in compressed air pipe, isentropic fan efficiency, optimum shaft size, and rate of methane desorption for coal. 4) Floyd C. Bossard and Associates, MIVENDES In addition to the ordinary airway resistance values, horsepower requirement, etc., the MIVENDES program also provides Heating and cooling of air Sources of heat include adiabatic compression, electromechanical equipment, explosives, and natural oxidation processes. Heating of mine inlet air and cooling of air on surface or underground by indirect cooling or evaporative cooling techniques are built in. Air psychrometry Psychrometric properties temperatures, humidity, moisture, apparent and specific air volume, gas constant, vapor pressure of water and dry air pressure. Diesel exhaust gases Concentrations of carbon monoxide, carbon dioxide, nitrous oxides, and nitrogen dioxide are predicted. Primary and booster fans, airflow, methane, and radon emissions. 5) Geomin, Ventilation Design This package provides an interactive design capability for three-dimensional networks with forced ventilation, natural ventilation or both. The program is interactive and includes 3-D graphics display facilities. Fans may be internal or external and can be treated as either constant or variable pressure sources. The user can specify minimum airflow requirements in network branches, such as for working faces. The output is flagged if the analytical results do not meet or exceed the predetermined value. 9

10 6) Hall, MINVENT, VENTDAT. The VENTDAT program is used to create the data file for MINVENT, the network analysis program. MINVENT uses the Hardy Cross principles and an incompressible flow network. Leakage is handled differently, because it is not accounted for the final balance. The quantity of air leaving the mine does not have to equal that entering. The program allows for changes in specific volume off the air caused by pressure, temperature or humidity changes; addition of compressed air; leakage through old workings or broken ground; and errors in the ventilation survey. Natural ventilation pressure can be included. Some user commented that the program works well if the network is fine tuned. Input is tedious because 12 items per airway are required although the program documentation states that it is not necessary to enter all the values. 7) HTME (Cerchar), P.C.Vent, VENDIS. The VENDIS program provides network calculation along with interactive graphic display. Network data can be entered by a combination of keyboard and digitizer entry. User input includes depth, resistance, temperature, and node (junction) location in three dimensions. Results can be displayed on the graphic screen and the user can modify the resistance, temperature, and display the new results. The scale of the network can be changed and the viewpoint can be change. When the network is displayed at certain angles, the result appears 3-dimensional. The network can also be output to a pen plotter for a paper copy. 8) MSHA, PENVEN, IDCEPS. The IDCEPS program interactively asks the user for data needed as input to the PENVEN program. The PENVEN program uses the ventilation program developed by Y. J. Wang and includes modifications added by MSHA. The changes include: The program was broken into modules. The input method was changed to a more flexible data acceptance. Conversion factors can be specified for input data. Fan curves are fitted with an unweighted least-squares fit and Newton's divided difference interpolating polynomial techniques is used. The user specifies the presumed operating point of each fan along with upper and lower limits. total pressures can be printed for all junctions. The user can input a starting guess at the balanced quantity distribution. The program will also construct a first guess. The program is in FORTRAN and has been run on a microcomputer by at least one company. 9) Penn. State University, MICROVENT (Disk #2) The mainframe code version is available in many conference proceedings and government contract reports. A microcomputer version named MICROVENT available on Disk #2 for the Apple computer is a limited version of the mainframe program. The micro version accepts only 50 branches and 5 different fans. Other programs on the disk include ventilation pressure survey calculation, network balancing, regulator sizing, ventilation of a 5-entry section, and cost analysis of ventilation shafts. 10

11 10) Virginia Tech, VENTSIM. The VENTSIM calculates air quantities, airway resistance, pressure drops, horsepower requirements the same the other programs do. A list of the program is available in government publications and a copy of a tape with the program is also available. The program was written for the mainframe and Virginia Tech. is currently developing a version for the microcomputer. 11) Chamber of Mines Research Organization (COMRO), ENVIRON (former HEATFLOW & VENTFLOW The ENVIRON was released in 1986 which combined both HEATFLOW and VENTFLOW into one program. It is an interactive computer program for the simultaneous analysis of heat loads and mine ventilation systems at all mining depths on both local and a mine-wide basis. It provides a full thermodynamic analysis of the mine and can be used to simulate existing ventilation and refrigeration systems, to identify the optimum mix of ventilation and refrigeration requirements, to carry out "what-if" studies. The program takes into account air density changes in deep mines including automatic adjusting of fan characteristics, natural ventilation pressures throughout the network, energy losses and associated costs for each airway and regular as well as the energy consumption and running cost of each fan. 12) MINE FIRE SIMULATOR Strata Mechanics Research Inst., Polish Academy of Science, Cracow, Poland The MINE FIRE SIMULATOR was developed by the Polish Academy of Science and was coded in Pascal. The program integrates three parts, a conventional network calculation program, a program to simulate the fire source (real-time heat and combustion products simulator), and a program to calculate the air temperature changes due to a fire. The package provides a dynamic (animated) representation of the fire's progress, a color-graphic visualization of the spread of combustion products, temperature, flow and other parameters throughout the ventilation system in real time. The program is fully interactive. All data are entered from the keyboard during program execution. 13) Other In-house Programs For example, CONSOL, Inc. has developed its in-house stand alone ventilation simulation program. The program is based on MFIRE but with all editing and plotting features similar to that of the AUTOCAD. It provides powerful tool for simulation and planning. For further information, please refer to other ventilation simulation literature and case studies. 11