Reference no: EM13373135
Control Engineering
You have to design a control system for an annealing furnace. The furnace is used to anneal special alloys. The alloys are heated to 640 °C by in an electrical resistance furnace and held at that temperature for your hours before being allowed to cool in the furnace. The cycle typically takes 8 hours (allowing for loading, heating, holding at temperature cooling and removing). The alloys are heated and cooled under an argon atmosphere to avoid excessive oxidation. Water cooling is provided to the panels of the furnace is Protect the refractories; the flowrate required is 265 liters/min. The cooling water is part of chilling circuit that ensures that the water is provided at 20 °C. A pump powered by an electric motor is used to provide the water to the circuit. The overall pressures losses in the circuit are around 100 kPa (not including a control valve) and the pump provides a pressure of kPa. The argon atmosphere is provided from pressurised again containers, through an on/off valve. It is important that the water and argon are flowing before the furnace starts heating the metal. Experience has shown that any significant overshoot of the annealing temperature set point is likely to cause problems with the surface quality of the alloys. SO operators of the current manual control system approach the set point cautiously. Current, metal ingots (on a trolley) are loaded and removed manually from the furnace, which has a door at one end /also manual, operated).
a) Select a suitable temperature measurement device for the furnace. Provide technical specifications of the device and justify your choice. Please describe any auxiliary equipment that needs to be considered.
b) Design an automatic control system for controlling the temperature in the furnace, drawing a block diagram showing the key elements and explaining how the proposed System would work.
c) Select the appropriately sized control valve, using the procedure described by Bolton. what sort of valve would suggest, Explain your choice.
d) A PLC has been selected to co-ordinate the sequences required for operating the furnace. Propose a ladder diagram for starting up the furnace that could be used for programming the PLC.
e) How would you propose to tune the temperature controller? Justify your choice.
f) Assuming the furnace follows the relationship derived on page 190 of Bolton, with the value of RC being 27 min, Rql is 1530 K and is 350 K, how would you expect the temperature profile of the furnace to Vary With time from room temperature to half its set Point (assume the heating element remains at maximum power during this time)• Provide the details of the calculations you have performed to form this relationship.