Last month, we discussed the need for project engineers to talk to process engineers about the water systems as a capital project takes shape. This months column discusses additional ways to bridge the communication gap between these two groups.
Assess suitability for service
Some industrial plants, such as refineries, have stringent engineering guidelines and sourcing for components and materials of construction. In the absence of clear guidance from the customer, the engineering design firm will follow its own internal design guidelines. A major constraint is a cost-competitive procurement process for equipment that selects lower cost materials, lower quality components and, sometimes, violates good design guidelines.
Consider the plant owner who agreed with the engineering firms recommendation to select a demineralizer system design sized for 150% of the maximum service flowrate because it reduced the capital cost in the competitive bid. The industry standard is 200% of the maximum service flowrate. After several years of operation, the plant replaced one unit with a larger-sized unit, resulting in a miss-matched set of demineralizer trains that have a common regeneration system programmaking it is impossible to optimize the regeneration sequence.
Assess operability and maintainability issues
Process engineers are experts on this subject and are responsible for solving the daily issues of operating and maintaining plant equipment.
Some design issues involve proper specification of online monitoring equipment and water storage tanks with sufficiently large working volumes to accommodate the dynamic treated-water demand profile. Project engineers should consult process engineers regarding location of sample points, chemical feed points and online analyzers. Process engineers know the application guidelines and the reliability and maintainability of these instruments.
Other problems are design issues. For example, the absence of a variable-speed drive on the recirculation pump on a reverse osmosis (RO) cleaning skid, compromises cleaning procedure for a multi-stage RO unit.
There is a tension when choosing new technologies. Process engineers vote no because they are unfamiliar with the operability and reliability of the new technologies and the cost is higher than conventional technologies. Conversely, project engineers will vote yes because the higher capital cost is amortized over the service life of the plant. The right way to evaluate new technology is suitability for service. For example, membrane filtration is a perfect pretreatment strategy to ensure reliable operation of RO units and packed-bed demineralizers. However, the capital cost is several time higher than the conventional multi-media filtration systems. But this incremental cost for new technology is a very small percentage of the total capital cost of the project. Conversely, specifying this technology in retrofit projects to replace conventional filtration is impossible because the hurdle for return-on-investment is too high.
Other site-specific limitations
The most common site-specific limitations are environmental and plot-plan issues. These operating issues may be forgotten or dismissed as unimportant. For example, a Canadian plant considered replacing its aging demineralizers with RO units until experiencing a rare shutdown of the entire plant on a cold winters day. I asked the question, Are we going to size the RO unit to operate on a cold start or are we going to install a supplemental bootstrap boiler to supply steam to heat the water and resize the RO for 25°C? The simpler, cheaper and more reliable option is demineralizers that are not so sensitive to water temperatures.
Identify the negotiable cost components
There is always a risk of cuts in project budgets. Discussion of the negotiable issues by process engineers during the project design is an excellent idea. A good example is the installation of a cleaning skid for RO units that uses flexible transfer hoses instead of permanently installed connections and, even worse, lacks quick-disconnect flanges. This configuration makes the cleaning process an onerous and time-consuming task. Consequently, the operators are unlikely to clean the RO at the right frequencynot a good choice to cut costs.
Project engineers must manage a huge number of technical issues for capital projects. Process engineers can add significant value to the design process by providing insights to operability and maintainability of various process designs and water treatment technologies. To have a successful plant project, both sets of engineers must talk to each other.
End of series
Part 1, June 2012. HP
Loraine A. Huchler is president of MarTech Systems, Inc., a consulting firm that provides technical advisory services to manage risk and optimize energy- and water-related systems including steam, cooling and wastewater in refineries and petrochemical plants. She holds a BS degree in chemical engineering, along with professional engineering licenses in New Jersey and Maryland, and is a certified management consultant.