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An overview of associated gas – its processing and treatment

Module 1

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Summary description of module�

  • General overview about the process and importance of it
  • Social and environmental issues of associated gas – its processing and treatment
  • Waste sources and contingency planning, i.e., sulfur

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Objectives

  • Analyze the importance of treating associated gas
  • Describe environmental issues/concerns at each stage of Associated gas production, including possible impacts on health and safety
  • Source the main concerns for trainees related to associated gas and industry in general

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Basic concepts

  • As identified in several publications, associated gas is defined as

Gas produced as a byproduct of crude oil production. Associated gas reserves are typically developed to produce crude oil, which pays for field development costs. Reserves typically produce at peak levels for a few years before declining.[1]

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Major concerns

  • In general, associated gas may contain
    • Sulfur above acceptable limits
    • Water content higher than natural gas fields
    • Oil droplets
    • Undesired capital investment
    • Major pitfalls for the oil production
    • Safety concerns
    • Environmental hiccups
    • Unsteady production (inconsistent intervals)

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Major concerns (continued)

  • Associated gas is considered a byproduct, which makes it unfavorable
  • The fastest disposal option is to flare it. “air pollution?”
  • Amounts of associated gas may not be adequate for re-injection
  • If entrained in oil, it may disturb oil production rates, with major affects on the auxiliary units used for pumping oil for further processing
  • Water content may be above limits. This adds environmental concerns, as wastewater requires treatment

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Gas processing plant block diagram

Figure 1. Gas Plant – Process Description

CEMS: SO2 Mass Emissions

H2S & SO2

High H2S

Gas Composition

Possible H2O Quality Measurement

Custody Transfer: Dew Point, H2S, Heating Value

LPG QC

Low H2S

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Gas sweetening – amine absorption

Figure 2. Natural gas treating process. Adapted from Instrument Technician

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Regenerate using heat input from a reboiler

Bubble cap trays: refer to glycol dehy. flow diagram

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Natural gas dehydration – adsorption technique

Figure 3. Adsorption Dehydration Two-Tower vs Three-Tower System

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Natural gas dehydration – glycol absorption technique

Figure 4. Dehydration With Glycol (Smith, 2013)

Remove the water

Heat exchanger

Regenerate the glycol

Lean glycol

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LPG recovery

Figure 5. Fractionation train. Adapted from Instrument Technician ILM, Gas Analyzers – Part A, 310304cA, (2016)

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Consider a GC with a multi-stream configuration

It’s all about boiling points and temp. control

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Sulfur recovery

Figure 6. Natural Gas Processing Plant. Adapted from Hauer, Randy (2013). Claus Sulfur Recovery [PowerPoint Slides]

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Sulfur Block

Flare stack with a small flame: things are going well today

CEMS sample point: about 40m

Sweetening & Dehy.

LPG Recovery

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The reaction furnace – incomplete combustion by intent

Figure 7. Natural Gas Processing Plant. Adapted from Hauer, Randy (2013). Claus Sulfur Recovery [PowerPoint Slides]

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925 °C – 1300 °C

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Figure 8. Natural Gas Processing Plant. Adapted from Hauer, Randy (2013). Claus Sulfur Recovery [PowerPoint Slides]

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H2S and SO2 Vapours

swept away to the incinerator

Molten sulfur

Measure for explosive levels of H2S

H2S measurement for feedforward

H2S and SO2 measurement for feedback trim or cascade

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Figure 9. Natural Gas Processing Plant. Adapted from Hauer, Randy (2013). Claus Sulfur Recovery [PowerPoint Slides]

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No SO2 breakthrough allowed – bad news for absorber

Low H2S <300 ppm = optimum absorber performance

Low H2S @ AT5 = low emissions

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Why do we bother recovering sulfur?

Keep It Clean

Figure 10 Stacked (Apergis, 2019)

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Most energy-demanding industries

  • Power generation consumes lots of energy, regardless of source. It’s considered a national security issue for countries, regardless of their land size and population
  • Certainly, refineries and petrochemical industries are also demanded highly
  • As a result, concepts of energy efficiency, energy optimization, and energy recovery were developed. The Energy Consumption concept, along with supported technologies and tools, were invented

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Several examples will be given as handouts.

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Energy-demanding industries will result in major CO2-containing waste streams

  • Power generation depends most on the actual burning of fossil fuel. Which results in major COx, NOx, SOx production
  • As the demand for clean operations increased, technologies to reduce harmful effluents increased too
  • The tools to determine the concentrations of those effluents are up to industries’ expectations of quality and online measurements

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Several examples will be given as handouts.

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Major methane-containing waste streams

  • It is very common among most countries, that the major methane-producing activity is landfill waste
  • Several countries have other activities or industries that produce methane as waste. Gas flaring is one activity, but if we focus on the major one, we should consider leaks - also called fugitive emissions - of associated gas/natural gas fields and pipelines. It is a major concern for countries, especially with the lack of maintenance activities

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Pollution mitigation strategies or waste stream minimization

  • Having strict environmental policies is one way to control pollution and minimize environmental issues
  • Several countries eliminated certain industries to stop the pollution coming from those industries
  • The use of coal for power generation was stopped completely and replaced with natural gas in several European countries and Canada
  • The concept of BAT “Best Available Technology” is implemented to minimize pollution. Several technologies disappeared and several others were modified due to the need for cleaner operations

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Key take-aways

  • Nothing is “waste” anymore; everything is valued
  • Associated gas and natural gas are similar in nature, process, waste streams, and environmental concerns
  • Associated gas is not a by-product; it is profitable with great potential
  • Sustainable projects’ execution must be the norm for new initiatives

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References

  1. Apergis, Jana (2019). Stacked-800x600[Image file.] Retrieved from: https://www.flickr.com/photos/jana_apergis/49176821476
  2. Government of Alberta – Advanced Education (2019). Instrument Technician ILM, Gas Analyzers – Part A, 310304cA
  3. Hauer, Randy (2013). AMETEK Claus Sulfur Recovery [PowerPoint slides]
  4. Moshfeghian, M (2015). Adsorption Dehydration: Two-Tower vs Three-Tower System. [Image file]. Retrieved from: https://www.jmcampbell.com/tip-of-the-month/wp-content/uploads/2015/10/fig2.png
  5. Smith, G (2013). Dehydration with glycol. [Image file]. Retrieved from: https://petrowiki.org/images/thumb/4/47/Vol3_Page_202_Image_0001.png/759px-Vol3_Page_202_Image_0001.png

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