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Download September 10, 2010

Energy, economy and environment: process simulation’s role in a difficult balancing act

A significant number of glycol dehydration units in gas processing are operated with excessive over-circulation of glycol (EPA, Natural Gas Star). Clearly the main reason behind this practice is the objective from operations personnel to ensure the dry gas water content is well within specs and to stay away from operating problems. However there are a number of undesirable impacts associated with this practice that range from increased energy consumption to increased toxic BTEX emissions. A Canadian report (CETAC-West, 2005) identified significant economic potential for optimization of glycol dehydrator systems with low or no capital investment required. The study estimated that there were 2,400 units suitable for such investigations on the basis that a number of these units are rather small and installed

in remote locations. The potential annual benefit for glycol dehydrators in Canada (assuming 50% success rate in optimizing these units) is approximately 372,000 tonnes of CO2eq eliminated and 180,000 E3M3 of natural gas savings.

The Energy Resources Conservation Board is the regulatory body from the Alberta Government and it has introduced in their requirements the concept of a Dehydrator Engineering and Operations Sheetv(DEOS). It incorporates a graph where the dry gas water content and the total benzene emissions from the unit are plotted as a function of glycol circulation rate (see Figure below).

This graph may be used to identify the glycol circulation rate that will achieve the required dry gas water  content and at the same time minimize the emissions of Benzene to atmosphere. Not shown in the  graph but also relevant to this discussion are the energy savings achieved in the glycol regeneration step as the circulation rate is reduced. If the unit is operating with a glycol circulation rate of say, 1.5 USGPM, it can be seen from the graph that  the dry gas water content is around 1 lb/MMSCF and the benzene emissions are close to 2.4 tonnes/year  (in Alberta, new dehydration units must be operated below 1 tonne/year benzene emissions). A reduction  in circulation rate to 0.7 USGPM will increase water content by 8% to 1.08 lb/MMSCF but result in a  reduction of benzene emissions of around 60% to about 1 tonne/year. 

Given the cost and difficulty of directly measuring the emissions on-site, most operators and regulatory  agencies have turned to process simulation tools to calculate the emissions. Furthermore, these graphs  can be automatically generated by setting up the model in HYSYS and exploiting the extensibility of the simulator to export the results to MS Excel or other software. 

This is but one illustration where simulation can be used to support better decision making in both  design and operations. By using simulation models together with reporting and analysis tools, it is possible to enhance our understanding of the various trade-offs between energy, economics and environmental goals that arise when optimizing process plants.

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By Alberto Alva Argaez, Ph.D, MBA

Alberto brings over 25 years of experience in chemical engineering research and process optimization for sustainability. As Senior Project Manager and Managing Partner, Alberto has worked across multiple industries to assist operating companies become more efficient in their use of energy and water. Alberto started his career as production engineer with Bayer and then spent ten years in Academia as research scientist and lecturer. In 1999 he joined Hyprotech/Aspentech in Calgary as product manager for conceptual design software tools and thermodynamics. Alberto later worked for seven years with Natural Resources Canada performing R&D and supporting energy-intensive industrial sectors through process integration and optimization projects. With Process Ecology Alberto has specialized in modeling and optimization for emissions reduction in the oil & gas sector. Alberto is a Biochemical Engineer and holds an MBA from ITESM and a Ph.D. in Chemical Engineering from UMIST, UK.



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