This is the first of four columns about educating people at your company on the importance of energy. This column focuses on your technical specialist.
Technical specialists concentrate on the health of your process. Your specialist can be a process engineer, corporate technology person or inside or outside consultant. This person has received extra training on the technology, whether on-the-job or through additional classes and seminars, and therefore can advise how the unit should perform. Because of this status, your technical specialist should also understand how the process uses energy and be aware of energy consumption and conservation when giving advice.
Training your specialist requires that you also understand how energy is used in the process. This will help when you talk to the specialist. However, you don't need to know all the nitty-gritty details.
Send a note to your expert and explain that you would like to talk about energy efficiency. Set an agenda to cover: feed preparation; reaction/process; feed effluent and products; and utility and equipment efficiency.
Feed preparation involves the steps to bring feed to the right temperature, pressure and quality for the unit's main function to work properly. It extends from the unit boundary to the reactor inlet. This is where energy is consumed to heat or cool or pressurize or depressurize material. Because these steps involve some heat input, I typically look at: how much energy is needed to get to the right conditions and how much energy is recovered from effluent or product streams. Stress to your process specialist that preparation steps are vital to energy efficiency.
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The reaction section involves exothermic or endothermic reactions. Feed conditions are set to optimize the process, but you should ask if the same result can be accomplished at a lower energy input. As an example, pressure may be a hydraulic constraint. Sometimes lower pressure separation requires less energy but product requirements demand higher pressure. Pressure also can be temperature related when trying to condense a gas, which may set limitations. So, feed conditions may be a variable that can lead to lower energy cost without product sacrifice.
The expert should understand using recycle or slopping. Recycle occurs when a stream contains unconverted or undesirable products or if minimum capacity of equipment is unsatisfied. Recycle always increases the process' energy requirements; controlling or minimizing recycle typically saves energy. Energy consumption must be part of the equation when determining recycle rates or the need to recycle.
Slop is created when products don't meet specification and the stream must be reprocessed. This typically happens on start-ups and shut downs, but can occur in finished product tanks. Such situations can and should be controlled and minimized. On stream analyzers tend to reduce slop effects by limiting the time material needs to be slopped. Start-up and shut down procedures also need to be reviewed to reduce the time material needs to be slopped. Slop production should always be a key performance indicator on any unit.
The feed effluent and products section runs from the reactor section outlet to the unit boundaries. It typically recovers energy or prepares streams for their next destination. In general the idea is to recover as much useful heat as possible without increasing another unit's requirement. One of my pet peeves is use of storage as an intermediate between process units. Typically, a stream needs to be cooled and depressured to enter storage. Storage preparation usually involves air or water cooling as the final step. The stream is then reheated and repressured before further processing. This is one hidden energy waster that can kill profitability. The more it's eliminated, the more efficient your process becomes. The process specialist must be made aware of this and work with you to reduce or eliminate this practice.
Utility and equipment efficiency involves operating heaters, pumps, steam, air and other utility equipment at the best performance. Previous columns have covered these items and I encourage constant monitoring of these systems by your specialist.
The important reminder to your specialist is that energy efficiency doesn't mean reducing product quality or unit capacity. In some cases, it can help increase improve the product or increase unit capacity. Educating the specialist on the key areas and economics can lead to major savings.
Gary Faagau is Chemical Processing's Energy Columnist. You can e-mail him at [email protected].
