Beans are hard grains that can take a while to get cooked and use a lot of fuel. There are some simple measures to reduce fuel consumption. Soak the beans in water overnight, and you will be able to cook them in around 10 or 15 minutes in a pressure cooker. Wait for the pressure to end by itself; the beans will keep cooking.
Some grains are so hard that you simply cannot cook them well without putting them to soak overnight. Chickpea is the classic example. But if you forget to let the grains soak overnight, there is still hope. Put them on the pan with water and light the fire. When it starts to boil, shut the fire off and close the lid. The beans will be softer as the ones you have left in water overnight, but much quicker. Then proceed to pressure cooking as told above.