Scott,
If you are truly interested in this as a business plan, look into the research that Washington State has done on turning
cardboard bales into biochar:
https://fortress.wa.gov/ecy/publications/documents/1207033.pdf pg 16. I think it warrants further study. With global shipping traffic coming to a virtual standstill now, there will soon be a back log of OCC or recycled cardboard as it is called in the industry piling up on the docks. Formerly, this was a big backhaul export to China. I know when I was running a business the ebb and flow of the price I received for my bales were directly tied to inbound traffic at the port. (The more goods coming into the country, the more empty containers that need to be filled to make it worth sending them back.) Right now, ship traffic, coming and going is dead. Recyclers will start charging business to haul away their recycle because they will have to drop it in a landfill with that market gone.
I was looking recently and starting to see places outside the US advertising their bales "free to pick up", so that trend has begun. A person could get all the feedstock they want for little to nothing, except the transport. There are several large kiln type that could adapt to the standard 60" bale. The limiting factor is the distribution. If you go down that road, put a sales presentation together on the "green" of recycle into char, and
sell the idea to existing dirt yards. They could sell a premium value added product to their existing market base much easier than you could develop a market.
Another option would be to approach lumber mills. They generate a lot of waste, but do a good job of converting their waste stream to a cash stream; but it is still cheap stock. The other thing is pulp. With construction in this country and in China also down in the extreme, the pulp product they once loaded into containers and shipped to the Pacific Rim is not moving, so pulp prices have tanked. At the price level they are at, it might be cost effective to burn pulp from the mills or buy the pulp stock from the foresters at even lower prices. Of course that depends on your geographic location. I don't know how many mills are near the Chicago area.
The mobile option could work, but remember, transportation costs will add up quick, unless they provide the feedstock.