Notes from Windward: #67


Big Score at The Bins

     Faithful readers of these Notes know that we rarely make a visit to Portland without taking a side trip to "The Bins," Goodwill's main sorting facility. We're big on reuse, and we rarely come away without a "find" or two, but yesterday's visit was especially fruitful.

     This summer we've focused on projects relating to hyper-integrated aquaponics since that was the aspect of our sustainability program that our summer interns were most interested in. Once the gardening season is done, we're looking forward to advancing our work on the conversion of biomass into methanol. One of the key challenges there involves the compression of gases such as carbon monoxide (CO) and hydrogen (H2), gases which are either poisonous, explosive or both. In addition, a project that we'll be undertaking next year involves the conversion of an insulated shipping container into a solar-powered walk-in cooler/freezer, a project which will involve the compression of ammonia (NH3), a gas which also is both poisonous and explosive.

     Most shop style air compressors use reciprocating pistons to compress air. That type of piston seals to the cylinder wall with metalic rings, and piston rings by their nature leak small amounts of the gas being compressed--the gas that leaks past the piston rings and out the crankcase is called "blow by." With air, that's no problem, but with CO and H2, that's a big problem. So instead of using piston based compessors, we'll be using a type of compressor that relies on hydraulic and pneumatic cylinders.

     In a hydraulic cylinder, a light-weight oil (called hydraulic fluid) enters a cylinder under pressure and pushes a piston along the length of the cylinder, and in pneumatic cyclinder compressed air does the same thing. Typically hydraulic cylinders are designed to handle pressure in excess of 2,000 pounds per square inch (psi), while pneumatic cylincers usually work with a top pressure of 250 psi.

     When you introduce pressure into the cylinder, force is exerted on the piston, and that pushes the shaft out the end of the cylinder. This process also works in reverse in that if you apply pressure to the shaft, the piston will compress the fluid (or gas) that's in the cylinder.

     One way a hydraulic compressor can be configured is to have a hydraulic cylinder operating a pneumatic cylinder. You could, for example, have a PV panel producing electricity, and use that to power an electric motor/hydraulic pump combination--the sort of arrangement you see controlling the lift gate on deliver trucks. The compressed fluid drives a hydraulic piston that's connected to the piston of a pneumatic cylinder.

     The gas we're most interested in compressing--producer gas, a combination of CO and H2--would then be cooled and stored in a holding tank at 250 psi; no noise, no leaks, no fuss.

     By using multiple stages, we can smoothly and safely compress gases--everything from air to methane--to better than 2000 psi, but these sort of cylinders don't come cheap and Windward does all this work out of pocket as funds allow, or as opportunties present themselves as one did this week at The Bins.


     The two large cylinders are 6" in diameter and 28" long, with the two smaller cylinders being four and three inches in diameter. Since we're going to want to compress a variety of gases in multiple locations, acquiring these additional cylinders will help speed those projects along nicely.

Notes From Windward - Index - Vol. 67