To run the mill at your rated capacity (or usual capacity) without running the turbine and with 100% process steam from the bypass line from the main steam header to the BPR, you will need to operate the boiler at your usual working pressure. If you run the boiler at, say 100 psig, you can throttle the steam pressure down to 45 psig but the flow rate of the steam will be very much lower. This is due to the difference in specific volume of steam at 100 psi (0.273 m3/kg) and 300 psi (01.100 m3/kg). Hence for the same pipe size, higher boiler operating pressure will deliver more steam to the BPR. The next bottleneck to getting enough quantity of steam for the milling processes is the sizes and length of the Main Steam pipe and the Bypass pipe. A 6 inches diameter steam pipe can deliver up to 16,193 kg per hour of steam at 10 barg. The same pipe can deliver about 30,250 kg per hour of steam @ 20 barg. In both cases, steam velocity taken at 40 m per sec, assuming saturated steam quality. For superheated steam, the velocity can be higher, up to 70 m per sec. It should be noted that high steam velocity in pipes will produce noise and erosion of the pipe wall. Say your normal milling capacity is 45 tons FFB per hour. For this you will need about 22.5 tons of steam @ 45 psig per hour. If you run the boiler at 10 barg, assuming 6 inches diameter steam pipe, you will only get about 16 tons of steam per hour. However if you run the boiler at 20 barg, you will get about 30 tons of steam per hour. Of course the final flow rate will depend on the length of main steam pipe, the number of bends and the pressure drop (caused by the velocity of steam). In most mill, the Bypass Steam Line from the Main Steam pipe to the BPR is only designed for make-up steam, not full flow of the required process steam. The PRV and the Bypass line at the PRV are usually smaller in diameter and may further restrict the flow of steam. So you will need to adjust the boiler operating pressure to get the optimal steam flow from your system. It should be noted that the steam in the BPR will be superheated after the reduction in pressure from the Main Steam pipe into the BPR. It may not be ideal for sterilization, but this is a compromise you will have to make to get the mill running until your turbine is repaired. Hope this will give you some idea to get the mill running as close to your rated capacity.