Interviews with Leading Engineers: Q&A with Christianto Wibowo on Energy Consumption

This is the second interview (in a series of five) of selected speakers for AIChE's upcoming Northeast Regional Conference at the Chem Show in November.

With the rising cost of energy and increased government oversight of greenhouse gas emissions, reducing energy consumption is a key topic for chemical engineers. While chemical engineers learn about balancing heat transfer across a chemical process, applying this knowledge in an effective way isn't always straightforward.

With over 10 years of experience consulting on process development projects, Christianto Wibowo has first-hand knowledge of how to approach energy management in the chemical plant. He is a senior member of AIChE and is actively involved in the Process Development Div. He holds a BS from Bandung Institute of Technology, Indonesia, and a PhD from the University of Massachusetts, Amherst, both in chemical engineering.

Wibowo recently spoke with Chemical Engineering Progress' assistant editor, Michelle Bryner, about energy management and his upcoming course on this topic at the 2011 Chem Show.

AIChE: What challenges do chemical engineers face when developing energy management plans?

Christianto Wibowo: Basically everybody is trying to save energy, even if they have been operating for many many years. We do a lot of consulting work in Japan and there has been a lot of pressure in Japan to reduce the energy consumption, CO2 generation, and so on. I think it applies everywhere in the world.

In order to manage energy consumption you cannot just say, okay how do we cut down the energy consumption without doing anything, without making any changes. We have to go back and look at the process. This is where the chemical engineers are heavily involved or should be heavily involved. We have to plan for a better way to utilize the energies throughout the plant. For example, is there any part of the process, maybe the equipment or maybe an entire process that is not using energy as efficiently as it should be. The other thing is, probably one part of the process is actually consuming energy in the sense that it needs some kind of heating or evaporation, but then there is probably some other processes within the same plant complex where energy needs to be removed from the system. If you can match some of those energy requirement and energy available for release then there can be potential energy savings right away. This kind of pattern or this kind of situation is what we really mean by developing an energy management plan.

AIChE: I understand in principle what you mean, but how would a chemical engineer approach this kind of project?

CW: The overall idea is to look at the current situation first, and ask what part of the processes are consuming energy, what part of the processes require removal of energy. And then you can look at what can be done to make modifications such that the overall energy consumption can be minimized. That applies firstly within one plant, whether there is internal energy exchange that can be done, but also sometimes we need to look at nearby plants, so within the same complex. Because of the proximity it is possible to install a heat exchanger that goes in the middle or something like that.

AIChE: What in your course will give chemical engineers what they need to develop energy management plans at their processing plants?

CW: Firstly, we are going to talk about the basic idea of pinch analysis. I'm sure that many people are quite familiar with pinch analysis but the emphasis of the course will be on how to look at your particular process and how to find those potential for energy reductions. The pinch analysis is basically looking at which part of the process is heated and cooled and then whether or not the temperature difference is such that the streams can exchange energy. Let's say that one stream needs to be heated from 50?C to 100?C and another stream needs to be cooled from 150?C to 120?C; this could be a potential match. But if you want to heat something from 100?C to 200?C and there is another stream to be cooled from 100?C to 50?C, then of course you cannot do it.

Secondly, we will talk about some examples of how to look for these things and how you should look at potential alternatives to modify the process because many people look at the pinch analysis as a matter of okay, how do I find all those potential matches and how do I make the most effective heat exchanger network to have maximum exchange to maximize the overall energy reduction. We try to go one step further. To us the question becomes: Is there any part of the process that can be changed such that the thermodynamic requirements also change?

Consider the example of a distillation column that operates at atmospheric pressure, and its distillate vapor stream condenses at 100?C. At this temperature, the pinch analysis shows that the release of energy from the condensation is not sufficient to heat another stream within the process to its target temperature. Some engineers will stop here and assume that their work is done. But a closer look could reveal that the stream would be useful if the condensation occurred at a higher temperature, say, 125?C. The condensation temperature could be increased, for instance, by operating the column at a higher pressure, or by compressing the distillate prior to condensation to increase the pressure (and thus the temperature) of the distillate stream.

AIChE: What's timely about the topic of energy management?

CW: The best answer for that is simply that right now everybody is trying to reduce energy, there is a high awareness that the energy resources are limited, environmental concerns to minimize the CO2 emission, and so on. It means that the pressure of doing this kind of thing is higher than ever. Because of that kind of situation and because of what chemical engineers are trained to do it's important for them to learn about energy management.

See the complete program for AIChE's Northeast Regional Conference at the Chem Show.

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