Don't forget to set an output range of PID in physical units as min...max Flow range in m3/h.
I assume you are talking about Fuel flow for combustion..., otherwise ignore the rest of my post.
If you are about to control Fuel flow, you need to program a cascade of 2 or 3 PID controllers. The upper PID will control Temperature . Output of upper PID in m3/h should be connected as external setpoint for slave PID that should control Fuel Flow. Output of Slave PID will be in range 0...100% probably connected to the Fuel control valve.
In fact, a slave Fuel flow control consists of twin PID controllers , one for Fuel flow and the second one for Air Flow. Both controllers must be interconnected by "crossed" interconnection in order to keep a proper fuel/air flow ratio.
A good choice for DCS-like PID are functions from BMI Library or PP Library.
Google for stoichiometric ratio. If you are a beginner , call a senior engineer.
The most important thing to remember is that if you mess this up you can blow things up. It sounds very like you're trying to control a furnace temperature / incinerator / boiler ? Typically, high temperature processes like boilers have strict regulatory requirements about who can work on them. You should not be making changes to the control system on your own without adequate supervision and sign-off on the changes.
Otherwise, yes - this is a job for PID control. Again, not a job for an unsupervised beginner. The rate of change limits on the PID controller output will take care of the increase / decrease in fuel flow rates. The P, I and D parameter settings will control the "closed loop" response time - ie how long the computer waits for a response from the process before making the next control action.
With the right supervision you should find that this is actually quite a simple program. Much more important is proper control tuning.