Noninvasive measurement and control system for use in hydrocarbon processing

A method of separating a heavy hydrocarbon from a light hydrocarbon, said method comprising the steps of:

• (a) charging a hydrocarbon-containing stream comprising the heavy hydrocarbon and the light hydrocarbon to a separator;
• (b) in the separator, separating the hydrocarbon-containing stream into a light hydrocarbon-rich stream and a heavy hydrocarbon-rich stream;
• (c) using a Raman spectrometer to analyze the light hydrocarbon-rich stream and determine a measured heavy hydrocarbon value indicative of the amount of the heavy hydrocarbon in the light hydrocarbon-rich stream;
• and
• (d) adjusting at least one operating parameter of the separator in response to the measured heavy hydrocarbon value.

A method of measuring the velocity of a fluid stream flowing through a conduit, said method comprising the steps of:

• (a) injecting a marker into the fluid stream flowing through the conduit at an injection location;
• (b) using a first Raman spectrometer to detect the presence of the marker in the fluid stream at a first measurement location downstream of the injection location;
• and
• (c) using a second Raman spectrometer to detect the presence of the marker in the fluid stream at a second measurement location downstream of the first measurement location.

A method of controlling a heavies removal column in a liquefied natural gas plant, said method comprising the steps of:

• (a) charging a natural gas stream comprising a light hydrocarbon and a heavy hydrocarbon to the heavies removal column;
• (b) simultaneously with step (a), charging a stripping gas stream to the heavies removal column;
• (c) in the heavies removal column, separating the natural gas stream into a light hydrocarbon-rich stream and a heavy hydrocarbon-rich stream;
• (d) using a Raman spectrometer to determine a measured heavy hydrocarbon value indicative of the amount of the heavy hydrocarbon in the light hydrocarbon-rich stream;
• and
• (e) adjusting the flow rate of the stripping gas to the heavies removal column in response to the measured heavy hydrocarbon value.

An apparatus for liquefying natural gas, said apparatus comprising:

• a final refrigeration cycle for producing liquefied natural gas at a temperature of less than about −25° F.;
• a conduit for carrying the produced liquefied natural gas away from the final refrigeration cycle;
• and
• a first Raman spectrometer coupled to the conduit and operable to measure at least one compositional property of the liquefied natural gas without removing the liquefied natural gas from the conduit.

An apparatus for liquefying natural gas, said apparatus comprising:

• a heavies removal column operable to remove at least one heavy hydrocarbon from the natural gas;
• a stripping gas conduit fluidly coupled to the heavies removal column and operable to deliver a stripping gas to the heavies removal column;
• a flow controller operable to control the flow of the stripping gas to the heavies removal column;
• a Raman spectrometer disposed downstream of the heavies removal column and operable to detect the heavy hydrocarbon in the natural gas stream and generate a signal indicative of the amount of the heavy hydrocarbon in the natural gas stream;
• and
• an automatic control device operably coupled to the flow controller and the Raman spectrometer,
• said automatic control device being programmed to adjust the flow controller in response to the signal generated by the Raman spectrometer.