I went for a long ride around various parts of Lima with Anita and Sylvia, two members of the religious group that is trying to establish soup kitchens, to see what opportunities there might be to help them save on fuel. We only spent a few minutes at each one, taking pictures and measurements. They were using lots of different fuels -- gas, when they could afford it, kerosene, wood, and even sawdust. They prefer gas because it´s somewhat cheaper than kerosene and a lot cleaner burning, but since one can only buy a tankful at a time (at a cost of about $10), when they´re short on cash (almost always) they have to settle for kerosene, which they buy a liter a time for less than a dollar.
Kerosene is burned in Primus stoves that look sort of like Coleman camping stoves, with a little pressurized tank and a manual pump. (See photo.) In some kitchens they prefer to use wood, but the neighbors always complain about the smoke. To burn sawdust they use a large empty cooking oil can that has a small door cut in one side. They place a large round stick upright in the middle of the container and pack sawdust all around it. Then they remove the log and remove the sawdust between the door and the hollow center, and start a fire in the middle. The door allows air to enter for combustion. Unfortunately the sawdust holds its shape well only if it is slightly wet, and that makes it burn much less efficiently, creating lots of smoke.
During the next few days I´ll develop a strategy for each kitchen (pot skirts, retained heat cookers, high efficiency wood stoves) and start teaching the people how to make and use the devices. The plan is that they will pay for the materials from their fuel savings.