I want to build a powerplant system with rate capacity 7 MW.
that to narrow for your question, design of thermo electric? nuclear? hydro?, step of what? better check the website first it might tell you something that you need?!
In most countries you have to be licensed to do this, as there are many ways to have a disaster, ie, an exploding boiler with loss of life. And you are obviously not qualified. So hire a professional to do this. .
I think you may not be qualified for this, to ask such a question. Maybe you meant design a system using a bought in boiler etc. This is hardly something you do by yourself. Most countries (probably all) require the designer, the manufacturer, the owner and the operator, as well as the boiler to be licensed and certified all along the way. Some would say get an Engineering Degree. In reality that on its own is not enough. You need the degree to get licensed, certainly, but also you need the experience and support structure to get it right. There is no room for mistakes. A boiler for a power station is specialised in the sense it uses superheated steam in a drive for efficiency, over 500C. It is best to leave boiler design to specialists and buy one ready made, it would cost more to develop your own than to buy. There is also control and various auxiliary systems that go with a boiler to help with efficiency and of course safety. There is a lot of energy stored up in a boiler, and if it is not right it can (and in the past often did) explode. Occasionally they still do (Chernobyl, probably the worst industrial accident ever, was a steam boiler explosion initially, caused by (I imagine gung-ho) people playing around to see if there was enough energy in the turbines running down to shut down a reactor. Nope, there wasn't. The boiler ran away, etc, etc..
