The melt shop is prepared to use cold DRI. The continuous DRI feeding system has already been designed to handle cold DRI and uses number of silos, EM vibro feeders, and few conveyor belts. The capacity of the DRI bins on top of the EAF can be scaled using weighing system when DRI feeding. As a rule, it is common to have the amount needed for one heat or little more.
The cold DRI is received from storage yards at any time as it is needed by the EAF. The handling system is designed with enough capacity to have the required amount of DRI and the same is stored before the EAF heat cycle starts.
The DRI storing silos will be installed on load cells. The load cells are of type shear beam or compression. The load cell signal will be summed in JB and connected to batching controller/weight indicator/PLC with special extension cable to transmitter modules, transmitter modules will be connected to batching controller. Through which it receives weight of each DRI silo. Provision is there to calibrate for required full scale.
These Transmitter modules are connected on LOCAL bus to the batching controller. The controller is state of the art and designed to handle up to six weigh silos .The controller has 16 digital outputs, 16 digital input and 4 nos. of analog outputs . The controller is programmed for batching of DRI in discharge batching modes as per the set point entered by the user. The controller has provision to control the feeding rate. The user needs to enter set point for feeding rate. The feeding rate is assumed continuous. If needed this rate can be made constant by varying the amplitude of EM/Motorized vibro feeders by calculating flow rate if user wishes.
The controller controls the feed rate of EM vibro feeders by use of its Coarse and Fine operation mode to adjust the speed of Motors (VFD control) / Firing angle. The controller is incorporated with serial ports to print a batch report on local serial printer. It also stores data of 1000 heat cycles for record purpose. It helps to maintain record of it for future analysis OR change in formulas if any require for raw material proportion to improve quality of the product.
The Continuous Feeding of cold DRI
When feeding cold DRI into an EAF, the rate at which it is to be fed depends on the available power, electrical and chemical. Typically, the amount fed is controlled by the specific feeding rate given by the ratio of the amount of DRI per unit time fed and the total power available inside the furnace as is shown in equation.
Specific Feeding Rate = DRI per unit time (kg/min) / Total power (Mw)
This ratio indicates the amount of DRI that can be fed into the EAF without causing DRI
Accumulation or liquid bath overheating for a given furnace depends on a given metallic charge quality, DRI and scrap. If the ratio is greater than this number, it means that there will be accumulation in the furnace since, there is not enough energy to melt the DRI being fed. On the other hand, if the ratio is less that the equilibrium ratio, it means that there will be more energy to heat the liquid bath since there is not enough DRI to melt.