This document is intended to assist engineers in the use of the Natural Gas Z-Factor computer program. This simple-to-use program utilizes the Microsoft Excel spreadsheet program and contains embedded macros that quickly solve a set of mathematical equations for a matural gas compressibility factor s ometimes called Z-Factor. This user's guide will explain the required input parameters, output parameters and the methods used to derive the compressibility factor. It will also describe the program's limitations and error checking capabilities. Example problems are given in both USC and SI units; these are intended to help users understand how the computer program can be used to find compressibility factors for everyday engineering problems.
The computer program was prepared with two purposes in mind. The first was to help patrons and engineers who are in need of a simple yet accurate method of determining compressibility factors of natural gas. Many of them rely on various charts or graphs developed many years ago by the Oil and Gas industry. Their primary interest is to get quick and accurate results. he second purpose of this program is to provide engineers with limited access to complex equations-of-state formulas with an alternate method of accurately determining compressibility factors. Many of these formulas are difficult to use and require knowledge of gas properties and composition. If the given information is limited or unreliable then Natural Gas Z-Factor can provide simple and reliable values with very little user input. The program is also well suited for applications involving sweet and sour gas if the composition is known or for application where only the gas specific gravity (also called relative density) is known. It is especially well suited to simple equipment sizing and performance problems with limited knowledge of the natural gas or if the application requires repetitive calculations to solve.
The program is based on a mathematical technique that digitally represents a graph commonly used in the Oil and Gas industry for sweet natural gas. A complete description of the technique is given in the referenced literature (1). The program also utilizes a technique (2) that corrects sweet natural gas compressibility factor if the gas contains either of the two sour gas constitutes, H2S and CO2. While this computer program may not be capable of deriving the gas compressibility for all service conditions, it can handle the vast majority. It is especially well suited for a wide range of operating conditions typically found in industry.
The Natural Gas Z-Factor computer program is easy to use and has proven to be practical when solving common engineering applications involving the need of gas compressibility factors. Merely load Excel onto you computer and open Natural Gas Z-Factor. The program is then ready to use. Note that the program contains macros that may require the user to override your system security protection.
Those with basic knowledge of natural gas thermodynamics and hydraulics will quickly adapt to the input parameter requirements and find how easy it is to modify the data for alternate solutions. Users will also find the results easy to understand. If additional knowledge is required of thermodynamics or gas hydraulics the user can review the Equations and Calculation Methods section and References section for helpful articles on these topics.
The computer program utilizes three Excel worksheets to display input parameters, output parameters, command buttons and warning messages. The three worksheets are Menu and Specific Gravity and Composition. The following sections will explan how to use each work sheet.
The Menu worksheet lists notes that briefly describe the program features, limitations and basis of calculations. Additionally, the Menu worksheet also allows the user to define one of two methods of determining a compressibility factor. Finally, this worksheet will also allow the user to choose the type of units displayed for input parameters.
The two options for determining the compressibility factor are as follows:
1. Specific Gravity Method 2. Composition Method.
The Menu worksheet will then display the method selected on the right-hand side of the command buttons. Immediately after the method is selected the user is automatically redirected to the selected method worksheet to begin input of required parameters.
It is recommended to select units of measure before proceeding with input of other parameters.
The Menuworksheet is also used to select the units of measure. The two options for units of measure are as follows:
1. United States Customary (USC) or 2. Systeme Internationale (SI)
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