Mukunth;
If that pressure cooker is a 20 quart size then as a starter or test one you should be okay with it.
Couple things that you'll need to help make it work with kitchen scraps.
For a test unit, you won't need the weight on the cooker, the mash itself will be heavy enough, instead get a screw in nipple fitting and a ploy type roll of tubing and run this to a smaller container so that the gas can bubble though it, this will take the deadly sulfur out of the gas as well and oxy out so the gas isn't explosive.
On another website (journey to forever) there has been tons of different studies done and there's even one by the person who is considered the father of modern day methods. Have a good look and then give it a try. One place you can help your's to work would be to find a person who has cats, Cats' urine contains ammonia and this is a jump starter for producing methane gas. It can be collected using news paper and the news paper shredded to help it brake down as well. When you start with the test unit, try and shred the scraps or mash them up before putting it in, this will help the stuff get going.
Do take a look over at the other site and enjoy the reading.
Most of the units built and not working is due to not following smoe simple guide lines.
Our daughter built one as a school science project using one of those 20 quart glass bottles and it worked once she got the correct method and mixture right.
Don't be in a hurry, it'll take about 2 weeks for it to start really going.
Hope this helps;
Bruce S