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By John Beath
JBE’s Refinery Water Use Study – What Matters?
As refinery wastewater discharge limits tighten and water scarcity issues (real and perceived) continue to impact license to operate and competition for water use (in some regions), the process of assessing water use is growing increasingly important. Further, certain aspects of water use relate to energy conservation (both onsite and offsite), and therefore also contribute to carbon footprint and costs.
This refinery water study was conducted as a way of determining the most effective opportunities for water use reduction by refineries. The project was initially envisioned as a study of a specific operating refinery, but was eventually converted to a study of a historical refinery (one that no longer operates) so that the data and process could be shared in more detail.
Previous efforts by others to study refinery water use have been based on varying amounts of site-specific data from multiple refineries across the United States, but these have allocated usage based on process unit yields as an approximation. This approach leads to compromises. For example, water usage for a butane overhead product cooler may be primarily assigned to the gasoline product based on unit yield, whereas its actual duty is clearly specific to the LPG product grouping.
Objectives
The specific objectives of the study were to:
The figure below illustrates why refinery water use, and efforts to optimize it is important.
Source: Texas Water Development Board (2015 usage data)
https://www.twdb.texas.gov/waterplanning/waterusesurvey/estimates/index.asp
The flow diagram for the study illustrates the focus areas selected. Those areas in blue contributed smaller (and already well-understood usages).
The results of the study showed that unit yields are not the best way to allocate water use to various products. This is important as a facility considers the implications of chnage a crude slate, say one from oil-shale fracturing where the light ends component may be higher.
Once the key usages have been determined, crudes with lower light ends fractions will demand less water use in a conventional refinery. If the crude slate cannot be adjusted, other process operation and revamp opportunities include:
Likewise for steam usage, a refinery might consider:
These tactics may also be helpful where discharge limits move a refinery towards reducing water use, or may otherwise require expensive water reuse measures to be engineered and constructed.
Please contact JBE if you are interested in more of the details of this study, or if you’d like to conduct one at your refinery or other facility.