|Our discussion about moisture laden dryer exhaust spurred some thinking about energy in general. This may seem trivial and also may be considered as already covered elsewhere, but it is worth bring to our attention once again. |
The thought is simply this: chips, pulp and recycled fiber reach our mills at ambient temperature and finished product leaves our mills at ambient temperature, therefore all heat used in our mills is simply process heat, although while necessary for the transformative processes of manufacture it, in and of itself, does not add value to the product. In other words, the finished products do not leave the mill hotter or cooler than the incoming raw materials.
The fact this leaves us with is that our continual requirements for heating or cooling energy reflect losses on the discharge side more than anything else. We need the heating or cooling effects to do something, but that something does not impart an increase or decrease in thermal energy in the product. In an ideal world, we could recover nearly all of this and reuse it.
A number of attempts have been made over the years to analyze the recovery of heat. One I remember from nearly thirty years ago was what was known as "pinch technology." There was a firm that I believe had both patents and trademarks on this particular form of energy analysis.
One of the larger historic mental blocks to this idea, however, comes from the days when particular energy forms, especially electricity, were extraordinarily expensive and also from the times when waste heat, fluids and air streams were simply discharged without treatment. These practices, many of which have been only grudgingly modified today as driven by regulatory mandates, often leaves discharge streams on the far side of the mill from input streams. Natural gravity flow of water affected this in liquid streams and a lack of amalgamated discharges affected it otherwise.
Perhaps today, at least from a theoretical standpoint, we need to think of mill design from an energy exchange centric point of view. In other words, if all process streams, liquid, and air, and friction induced-streams (lubricating systems), were thought of as exchanging heat in one central location, imagine it as its own building in the utility island, could we build an extremely low energy mill? Would the transport costs and/or the lack of significant temperature differentials make this a poor or a good investment?
We don't know any of the answers to these very interesting questions. However, we expect to spend some of our time together in 2013 discussing and exploring them further.
As always, your comments will be appreciated.
Brian Brogdon, Ph.D.
You know you have succeeded in capturing water and heat when your mill has no plume at all. If you want an example, drive to Syracuse and try to find the RockTenn Solvay mill the old way. Tough to do because there are no plumes from the 3 machines. There is only one roof penetration for each machine for ALL of the process vents. This includes the hood, vacuum systems, mist control, pulper exhausts and vapor hoods. How you stage all of this is critical to retaining heat and water while exhausting a zero condensing air stream.
The original system was installed roughly 15 or more years ago because the municipal road next to the mill would ice over from mill exhaust systems during the winter. It has more than paid for itself in energy and water conservation as a side benefit. This mill buys water and pays for effluent discharge so the math was simple for the water side.
The original thinker behind all of this was Lauri Coulson who designed a rather unorthodox process HVAC system to get the job done. Unfortunately it's so unorthodox that it hasn't been adopted by main stream suppliers (yet) because they don't know how to sell the concept.
By the way, do you think a single centralized heat/water processing system is lighter than conventional systems? You can bet it is!
Regards, Bryan Creagan
Seems to me that one could "wring" the water out of the hot air in a relatively small, cyclonic device with the introduction of cold exterior air to condense the water. In addition to the physical cyclonic action, wouldn't raising the pressure of the air tend to drop out the water? Of course, one would need to filter the air - or recovered water - due to impurities such as wood dust, insects, etc. Then, it might be possible to recycle the "dry" air back to the building / process thereby reducing the need to heat cold air. All of this would make life safer for those of us with glasses to prevent fog ups. So, a collector / duct, a cyclone device, a drain system to capture & use the water, and a duct to send the air back to the building inlet, and problem at least improved.
Regards, Bill Adams
The idea below works only in a non-contact air-to-air heat exchange: moisture will condense out of the dryer exhaust as it cools. The condensed water is not as clean as you may think, as some VOC's and dust are entrained, but that exchange is an effective means of pre-heating outside air. If the two streams of air were actually mixed as proposed, the mixture will be further away from saturation than the dryer exhaust alone and moisture will not condense at all.
Send us your comments!