1311 Fuel Consumption

Fuel consumption is typically reported as the quantity of fuel consumed per hour based on a specified load. It is impossible for any DG developer to provide the customer with an exact calculation of fuel requirements unless the time-weighted load usage is specified. As such, the manufacturer usually reports the maximum fuel consumption at full (100%) load. Some generators at no load typically use about half of the fuel used at full load. This linear relationship between fuel usage and load allows a reasonable estimate of fuel consumption over an assumed range of operating conditions. Thus,

Fuel consumption = (estimated load amps/max. generator output) x 0.5 x max. fuel consumption + 50% of max. fuel consumption

Other technologies use only a small fraction of the full-load fuel. Each technology differs, and specific information should be used for correct economic and thermal analyses.

13.2 Natural Gas and Natural Gas Derivatives

Natural gas and associated gas, the gas produced in conjunction with oil production, is piped to field gas plants near the wellhead. Hydrogen sulfide, carbon dioxide, nitrogen, water, and other contaminates are removed, and a significant amount of NGL, essentially the C3+ and C2+ hydrocarbons, is stripped from the natural gas to meet pipeline specifications. There are over 700 field gas plants in Canada. The majority are located in Alberta. However, not all gas plants produce significant quantities of NGL. The average propane recovery is 0.04 units of NGL per unit of raw gas produced.

The processed natural gas is sent via pipeline from field gas plants to gas straddle plants to recover residual C3+ and C2+ components. The straddle plants produce one-third of the total propane produced from natural gas production. Separation facilities fractionate the NGL mixture into components for marketing. The separated fractions are moved by truck to local markets and through pipelines or by rail to distant markets. In countries with well developed gas pipeline infrastructures, such as the lower 48 states of the U.S. and western Canada, natural gas is processed and sold to customers who contract with pipelines to transport the gas.

In their pure form, NGLs are known as spec products. Ethane plus, known as C2+, is a mixture of ethane, propane, butane, and a small amount of pen-tanes and higher molecular weight hydrocarbons called pentane plus. Propane plus, known as C3+, is a mixture of propane, butane, and pentane plus. LPG is generally a byproduct of oil refinery processes and consists principally of propane and butane. As with NGL extraction processes, refinery propane extraction can be varied to meet demand. LPG is comprised of a mixture of hydrocarbons containing varying degrees of propane and butane.

The decision to process natural gas is dependent on both economics and pipeline specifications. Gas processing plants generally operate off the margin between the price of natural gas and price of NGLs. Through much of the 1980s and 1990s, this margin spread was either nonexistent or was too small to support the operating costs of processing plants. Consequently, gas processors tended to process only the minimum quantity of natural gas necessary to meet pipeline specifications. Energy companies have been generally unsuccessful in increasing market demand for natural gas liquids as rapidly as the demand for natural gas.

TABLE 13.1

Description of Natural Gas and Natural Gas Liquid Fuels (Methane, Ethane, and Propane)

Ignition temperature, °F (°C) 920-1020° (493-549°)

Maximum flame temperature, °F (°C) 3600° (1982°)

Percentage of gas in air for maximum flame temperature 4.4%

Lower and upper limits of flammability (percentage of gas in air) 2.4 to 9.5%

Octane number (iso-octane = 100) 97 to 125

Solar Stirling Engine Basics Explained

Solar Stirling Engine Basics Explained

The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.

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