Oil and gas production handbook An introduction to oil ... - ABB Group
Oil and gas production handbook An introduction to oil ... - ABB Group
Oil and gas production handbook An introduction to oil ... - ABB Group
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5.3.4 Nitrogen rejection<br />
Excessive nitrogen is removed by cryogenic distillation <strong>and</strong> higher<br />
concentrations are removed by absorption with lean <strong>oil</strong> or another special<br />
solvent if a smaller fraction is detected. (See acid <strong>gas</strong> removal for both<br />
principles). Cryogenic removal also permits <strong>production</strong> of helium, if present,<br />
as a valuable byproduct.<br />
5.3.5 NGL recovery <strong>and</strong> treatment<br />
Remaining NGLs are recovered from the <strong>gas</strong> stream in most modern plants<br />
by a cryogenic turbo exp<strong>and</strong>er-based process followed by a fractionating<br />
process. This process leads the cooled NGLs though distillation columns<br />
called de-ethanizer, de-propanizer <strong>and</strong> de-butanizer, <strong>to</strong> extract ethane,<br />
propane <strong>and</strong> butane respectively <strong>and</strong> leave a residual stream of pentane <strong>and</strong><br />
higher hydrocarbons.<br />
The final step is <strong>to</strong> remove mercaptans (smelly organic <strong>gas</strong>es, e.g., CH 3 SH)<br />
if present, in a sweetening process based on molecular sieves adsorption or<br />
catalytic oxidization such as Merox mercaptan oxidization or Sulfrex, where<br />
the main difference is the type of catalyst.<br />
5.3.6 Sales <strong>gas</strong> specifications<br />
The exact sales <strong>gas</strong> specification is specified by pipeline opera<strong>to</strong>rs <strong>and</strong><br />
distribu<strong>to</strong>rs. Typical st<strong>and</strong>ard sales <strong>gas</strong> requirements use the following<br />
parameters:<br />
Volume is measured in st<strong>and</strong>ard cubic meters (scm) defined as 1 m 3 at 0 ºC<br />
<strong>and</strong> 101.325 kPa or st<strong>and</strong>ard cubic feet (scf) as 1 ft 3 at 60 °F (16 °C) <strong>and</strong><br />
14.73 PSIA.<br />
Calorific value specifies the <strong>to</strong>tal amount of energy per unit generated<br />
during combustion of the <strong>gas</strong>. The value is used <strong>to</strong> calculate the amount of<br />
energy delivered. Several values are listed:<br />
• Gross calorific value or gross heat of combustion is the heat<br />
released when a specific quantity of fuel in mixture with air is ignited<br />
<strong>and</strong> the end products have returned <strong>to</strong> the initial temperature,<br />
normally 25 ºC. EU specifications are typically 38.8 MJ (10.8 kWh)<br />
±5% per scm. In the US 1030 BTU ±5% per scf.<br />
• Net calorific value or net heat of combustion is the net heat<br />
generated when the water vapor in the <strong>gas</strong> does not condense<br />
(water forms during combustion) <strong>and</strong> can be 10% lower.<br />
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