| 摘要 |
Supervisory control system including an arrangement and process for controlling the operation of a dryer for the continuous adiabatic drying of a moist solid product with heated air for direct or close control of the dried product moisture, with mechanisms and counterpart steps, preferably using function blocks in a logic arrangement, for determining the wet bulb temperature of the dryer air from measurements of the dryer air outlet dry bulb temperature and outlet relative humidity, for determining from measurements of the inlet and outlet air dry bulb temperatures and the determined wet bulb temperature a supervisory value corresponding to the heating fuel supply rate needed to heat the air to an optimum dry bulb temperature operating value for drying the product to a predetermined moisture content at predetermined airflow and product feed rate and for producing from the supervisory value in relation to such outlet temperature measurement a corresponding supervisory signal, and for supervisory control of the supervisory signal to prevent product scorching, overdrying and underdrying when load variations are encountered in the operation, by limiting the fuel rate to a maximum rate to prevent the inlet temperature from exceeding a scorch preventing maximum level, by limiting the fuel rate to a minimum rate and reducing the air flow rate from the predetermined rate and adjusting the supervisory value and supervisory signal by feed back control when the inlet temperature needed would otherwise go below a minimum predetermined level to prevent overdrying, and by reducing the product feedrate to prevent product underdrying when the required inlet temperature operating value for achieving the desired final product moisture content would otherwise exceed the scorch preventing level and the inlet temperature is thereby limited to the scorch preventing level. |
