Before making this nitrogen generator you should know a few things. The unit is at least 300lbs when complete. You will be dealing with pressures close to 150 psi. You will need access to welding equipment and possibly steel plate rollers.
The PSA consists of two tower beds, solenoid pneumatic valves and a controller. I sized my unit to deliver about 30 L/min of 98% or better purity N2. The bed is made from an 8" schedule 40 steel pipe at 33" long. The top and bottom has a welded low-pressure (150 psi) steel flange plate. The botto is an 8" 150# raised-face slip-on flange and the top is an 8" 150# raised-face blind flange. A gasket helps seal this plate with a solid blank flange plate on top. A hole is drilled in the center to accept a 1/4" steel nipple, which you weld to the outer, removable plate. You can go to 3/8", but this did not seem necessary for the flows I'm using, and this increases the costs of the other hardware and pipes.
Each of the two towers holds 20kg of CMS-200 or CMS-H. You need to prevent these grains from emptying through the plumbing. You accomplish this with an insertible steel screen. You need to fashion a ring of steel that will just fit the inner diameter of the tower. Weld some steel screening onto this ring using whatever method works best for you. The screening needs to have holes about 1mm in size so the CMS grains do not pass through. This still ensures good airflow. As an added precaution you will use 10-12 MERV air-conditioning filter paper to trap dust from degrading the CMS.
Insert the bottom screen component. I welded two loops of steel on opposite sides so I could drop and retrieve the screen with two long poles. The ring holding the screen fits snuggly, so you will not be able to reach down with your hands and grap it out. Next, drop the filter paper and then fill the tower almost to the top with the CMS. Now, place another layer of the filter paper, followed by the screen. There should be now way for the grains to drop through the bottom or get discharged out from the top. Screw down the top plate.
As mentioned above, these towers are very heavy. I have mine sitting on a rack with large wheels on the bottom so I can roll it around. You will not be carrying this up and down flights of stairs, so pick a good resting place to keep it.
Below are pictures showing the bed with the screen. Again, this screening is duplicated on the bottom, except there are steel loops on the insertable ring to allow for extraction.