Monday, July 29, 2013

Re-using Waste in Forward Operating Bases

One of the many unsexy challenges facing servicemen and women deployed in nations like Afghanistan is the disposal of the incredible amount of material waste that deployments produce.   Many smaller Forward Operating Bases (FOBs) are relegated to simply burning their waste, ranging from packaging material from care packages, to unneeded paper products, and, some of the least pleasant, human waste.   What I would like to propose is a technology that might aid in reducing the problems associated with waste disposal on a FOB.
Rocket Stoves are considered one of the most efficient means of utilizing traditional fuel sources, including, wood, grass, and dung.  The objective is to develop a product design envelope for a rocket stove that works in multiple ways to help manage waste production in remote areas.  In Figure 1 is an simple example of a rocket stove.  Fuel burns in the combustion chamber with the smoke from the fire being pulled into the larger volume chimney, the placement of the chimney promotes strong air flow aiding in the burn process, the lay out also allows for greater use of the energy produced by the burn.  (the red lines show the path of air through the system)

Figure 1:  Basic Rocket Stove
The high temperature burn produced in the combustion chamber of a standard rocket stove is most likely enough to promote a cleaner burn process than an open pit burn more can be done.  According to a 2010 US Army Corps of Engineers report the average warfighter will produce roughly one third of a pound of waste per day.  Often human waste is what is being disposed of in open pit burns.  The platform shown in Figure 2 is a preliminary concept for handling human waste.



Fig 2:  the modified rocket stove design
The first major change you should notice between Fig 1 and Fig 2 are the red radiator pips now surrounding the chimney segment of rocket-stove, the purpose of the radiator pipes is to allow personnel to take greater advantage of the thermal energy produced by the stove.  In this particular approach I assumed that the quality* of the heat produced by the rocket stove is not great enough to warrant a fully fledged steam generator .  Based on my assumption about heat quality I suggest that between the radiator pipes and the chimney section would be a network of thermo-electric generators (TEG), making the platform a true co-gen system.  The heat that is carried away from the chimney system allows for a maximum delta T, improving the performance of the TEG, this waste heat, while of a lower quality still has a great amount of value, I will emphasize the nastier sounding narrative that I believe has the greatest use.  After absorbing sufficient thermal energy from the rocket stove the working fluid will need to transfer its heat somewhere, that somewhere could be the dehydration of poop (sorry I wanted to say that for ever and this isn't a fully professional document so work with me).  Boiling water, as many home chocoletiers know, is one of the most effective ways to keep a temperature constant, human waste contains an incredible amount of water.  As the intent of this design is to reduce smell it would be silly to try dehydrating the liquid waste in an open environment consequently the dehydration chamber's off gas would be pulled into the air intake of the combustion chamber, causing the materials to be combusted into less noxious component materials. (I hope)  After the waste has been dehydrated enough it can now be more thoroughly disposed of by being utilized as a fuel source.
(I need to insert a thermal diagram of the cooling deal)


*Energy Quality relates to how easily you can get energy to change from form A to form B.  In the case of boiling water you've already changed the form once and to said steam into electricity means you are going from B to C, doing this by means of a turbine generator, is most likely not possible.

** I totally forgot to note the suggestion of having TEGs and a heat exchanger in the exhaust/intake section of the design.  Darn.  At least one other Alaskan likes the idea of a TEG in a stove exhaust.

This post was originally intended to be a section on suggesting my own take for developing a rocket stove for rural communities that would serve as a hot water heater and electrical generator for homes.  For whatever reason the narrative of a co-gen platform at an FOB felt easier to write, but both applications are viable, the only difference would be the statistics and sources I referenced.


No comments:

Post a Comment