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It is widely accepted that global natural gas demand will continue to grow for the foreseeable future, possibly doubling every decade. Major new upstream developments, together with midstream transportation systems and downstream feedstock projects, are already progressing in all world areas. As this gas revolution evolves, there will be a dramatic rise in the requirement for high-accuracy measurement at every point in the gas value chain (Figure 1). Within these categories, there is a huge array of different gas-metering applications and a similar number of potential solutions. This can lead to confusion when selecting the optimum solution for the application.
Introduction: Gas – The Fuel of the 21st Century Natural gas is the fastest growing primary energy source. Its use is projected to double between 1999 and 2020. The mix of fossil fuels used to provide energy and petrochemicals is shifting toward natural gas (or just "gas") and away from coal. Natural gas is the more hydrogen-rich fuel. The worldwide increase in demand for natural gas is driven by the abundance of natural gas reserves, continued technological advances in exploration and production, and the desire for low-carbon fuels and cleaner air. The global demand for gas is increasing at more than twice the rate of oil demand. In the near future, one can envision an economy powered by gas. There are approximately 150 trillion m3 of proven natural gas reserves available worldwide as of the year 2000. At current consumption rates, the worldwide reserves-to-production ratio for gas is approximately 65 years, compared with 38 years for crude oil. Many factors support the growth of the use of gas. Natural gas is a clean-burning fuel. It has a higher ratio of hydrogen to carbon compared with fuels like coal and oil; therefore, it releases less carbon dioxide per unit energy output compared with oil and coal. If sulfur is present in natural gas, it is removed at the source gas-processing facility. Additionally, natural gas can be burned with more controlled flame temperature compared with other fossil fuels, resulting in lower NOx emissions. These inherent properties of natural gas make it the fuel of choice compared with coal and oil for achieving reductions in greenhouse emissions. On the down side, the disadvantage of natural gas is that it is more expensive to transport. The calorific value of oil in relation to the volume it occupies, at ambient conditions, is 1,000 times greater than that of gas. Fundamentally, it is this handicap that the oil and gas industry has to address for gas to fulfill its potential as the fuel of the near future. This limitation on gas usage is evident from the fact that only 23% of the world gas production is traded internationally vs. 57% for oil. Gas exploration has generally been limited by the cost to transport the gas to the market; hence, the current reserves of natural gas significantly underestimate the available gas resources. Continued technology development is lowering the cost of production, which, when combined with advances in technology for transporting gas and gas-based products to the market, has increased the focus on gas exploration.
Table 1 shows the gas-field-size requirements and typical world-scale plant sizes for some of the gas utilization options. The gas-field-size requirements are based on a single-train plant with a 20-year life. It is possible to have multiple-train plants, which will require larger-sized gas fields; however, under these circumstances, the impact of the additional production on the product market should be evaluated. A combination of different gas monetization options also can be used depending on the available gas reserves. Table 2 compares the total market size for the different products for year 2001.
Natural gas reserves are plentiful around the world, but many are too small or too remote from sizable population centers to be developed economically. Stranded gas is essentially gas that is wasted or unused. Estimates of remote or stranded gas reserves range from 40 to 60% of the world's proven gas reserves. The local market for gas is usually too small, or the gas field is too far from the industrialized markets. Sometimes excess gas reserves can be classified as stranded because they may result in oversupply of the market.
Natural gas is of little value unless it can be brought from the wellhead to the customer, who may be several thousand kilometers from the source. Because natural gas is relatively low in energy content per unit volume, it is expensive to transport. The cost to transport energy in the form of gas is significantly greater than for oil. This is one of the key hurdles to the increased use of gas. The most popular way to move gas from the source to the consumer is through pipelines.
A relief system is an emergency system for discharging gas during abnormal conditions, by manual or controlled means or by an automatic pressure relief valve from a pressurized vessel or piping system, to the atmosphere to relieve pressures in excess of the maximum allowable working pressure (MAWP). A scrubbing vessel should be provided for liquid separation if liquid hydrocarbons are anticipated. The relief-system outlet may be either vented or flared. If designed properly, vent or flare emergency-relief systems from pressure vessels may be combined. Some facilities include systems for depressuring pressure vessels in the event of an emergency shutdown. The depressuring-system control valves may be arranged to discharge into the vent, flare, or relief systems.
Natural gas is the feedstock used in most of the world's production of methanol. Methanol is a primary liquid petrochemical made from renewable and nonrenewable fossil fuels containing carbon and hydrogen. Containing one carbon atom, methanol is the simplest alcohol. It is a colorless, tasteless liquid and is commonly known as "wood alcohol." Stranded gas can be monetized by producing chemical (or fuel grade) methanol and transporting it to the market.
Converting gas to liquids (GTL) through the Fischer-Tropsch (FT) route to monetize stranded gas has received increasing attention over the past few years. FT technology is a process that rearranges carbon and hydrogen molecules in a manner that produces a liquid, heavier hydrocarbon molecule. In general, GTL through the FT route refers to technology for the conversion of natural gas to liquid; however, GTL is a generic term applicable to any hydrocarbon feedstock. This page focuses on GTL processes based on natural gas feedstock. FT chemistry originated during the early 1920s from the pioneering work of Franz Fischer and Hans Tropsch at the Kaiser Wilhelm Inst.