Post 2: Top 4 Factors to Consider When Specifying and Designing Geomembrane Systems for High-Temperature Applications

Series: Geomembrane Selection & Design for Elevated Temperature Containment
Post 2: Top 4 Factors to Consider When Specifying and Designing Geomembrane Systems for High-Temperature Applications


In Post 1, we looked at how an engineer might encounter a containment application at elevated temperatures. The mechanisms that could cause more rapid chemical reactions were also reviewed, and elevated temperature was noted as one of the major drivers.

To properly select and design a geomembrane containment system, first define the application:

• Type:  Impoundment, etc.; physical characteristics
• Liquid characterization
• Temperature and occurrence: Is it continuous?
• Source of elevated temperature: Incoming temperature, containment temperature. Is the temperature of the containment maintained? Temperature distribution in containment?
• Air temperature
• Detention time and characteristics

The occurrence of the temperature is very important.  A liquid entering a geomembrane lined structure at an elevated temperature and then naturally decreasing is a much different application than one where the liquid remains at temperature throughout the containment. Further, as stated in the first post of this series, temperature is usually discussed in the context of water, not water solutions or other liquids. The behavior of polymers will be quite different in these applications. Generally speaking, there are three types of geomembrane products promoted for “high temperature” applications:

1. Modified Polyethylenes - Normal polyethylenes in the geomembrane industry are promoted with an upper temperature limit of 140^o F (60^o C), assumed for water. Some others used in specialized small diameter pipe applications have been modified to increase the tie molecules (surfactant blog to be posted in future will give additional detail) to prolong the ductile mechanical failure with subsequent brittle creep and chemical failure. Creep and chemical failure are accelerated by several environmental factors including elevated temperature and fatigue. Modified PEs compensate by over-stabilizing, which in effect adds additional tie molecules to prolong the onset of Creep rupture and chemical failure.
2. Ethylene Copolymers - Trade named XR-5®, the material is non crystalline and by its nature has high chemical and thermal resistance. An amorphous structure is stabilized by the interaction of the principal molecules; i.e., the random structure does not rely on intermediate molecules for stability and thus is not subject to failure due to depleted, structural additives. The XR-5 geomembrane is rated for sustained contact with water at 180^o F (82^o F). The XR-5 also has extremely low thermal expansion-contraction characteristics which is essential in most applications including elevated and/or cyclic thermal conditions.
   
   
   
                                                                      XR-5 Geomembrane Lined Impoundment
                                                                       Oil and Gas Industry. Mississippi, USA 
   
   
3. Fluoropolymers – Either in rigid or more flexible geomembrane form, fluoropolymers offer high heat resistance but present difficulties in handling, welding, and survivability. Because they are also about an order of magnitude higher in cost than other geomembranes, their use is extremely limited.

1. Nothing defines performance like data; past data and specific data. Geomembrane compatibility will be different with different solutions, but interpretation from past data is extremely helpful when evaluating a geomembrane.
2. Look at geomembrane expected reactions to the elevated temperature solution, based on the content of the geomembrane.
   
3. If the high temperature is intermittent, more options exist for the geomembrane selection. Consider engineered controls of the application such as heat dissipating features (splash aeration, rapid mixing, controlled releases, recycling/dilution) where the site and process allow. High inlet temperature and the need for rapid heat reduction is common. Also consider protective layers to provide insulation. For instance, we have seen applications where soil-cement covered the XR-5 as an additional safety factor. We also commonly see insulation between the floors of heated tanks and a geomembrane, for additional heat protection.
   
4. When specifying a geomembrane, be specific about the product which has the track record and supporting data which you believe will support the project objectives. Do not accept a commodity approach to a critical application.