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Recently, more and more attention has been paid on alternative ironmaking processes due to the sustainable development. Aimed for the development of a new direct reduction technology, PSH process, the effects of reducing time on the metallization degree (MD) of carbothermic reduction of tall pellets bed at high temperature (1 500°C) are investigated at lab-scale in present work. The experimental results show, (1) In case of 50 min of reducing time, the MD of bottom layer DRI (Direct Reduced Iron) is lower, about 13%. MD of total pellets bed is about 58%. (2) In case of 60 min, the MD of bottom layer DRI increases to 63%. MD of total pellets bed increases to 80%. But for this case, the longer reducing time may result in some disadvantage, e.g. re-oxidation of top layer DRI, low efficiency of thermal energy, and low productivity. (3) Hot charge can obviously increase the metallization degree of DRI, especially for the bottom layers. In case of 50 min, compared with cold charge operation, the MD of bottom layer increases from 13% to 78%. Then the MD of total DRI bed increases from 58% to 85% by hot charge operation. Therefore, 50 min and hot charge are proposed based on the investigation in present work. These experimental results can give some theoretical references for the development of PSH process in future.KEY WORDS: metallization degree; carbothermic reduction; reducing time; tall pellets bed.It should be pointed out that there are two core technologies for application and achievement of PSH process, (1) prevention of newly formed DRI (Direct Reduced Iron) from re-oxidation by fully combusted gas. (2) Fast heat transfer from the top to bottom of pellets bed.(1) The newly formed DRI at the top of the bed is protected from re-oxidation by the upward gas flow (basically the gas is CO rich) generated during the reduction of pellets International, Vol. 56 (2016), No. 1in the tall bed, and enhanced by the high volatile coal in green ball over a longer period of the reducing time (refer to the C/O ratio in ore/coal composite pellets in section 2.1 "Raw Materials"). So, tall pellets bed is one of the operational characteristics of PSH process.(2) From the view point of the process control, the radiation heat transfer from heating source to the bottom of bed is the critical step of the process. The temperature of heat source is the most important variable for enhancing the rate of heat transfer in the whole system, because the intensity of thermal radiation is proportional to T 4 of heat source. Therefore, high temperature is also one of the operational characteristics of PSH process, which can drastically improve heat transfer in the process. In addition, the shrinkage of the newly formed DRI in top layers at high temperature (1 500°C) is the key for radiation heat transfer, because the shrinkage can result in a larger space for the passage of radiative heat flux (Section 3.2 in this paper for details).Therefore, PSH process is considered to produce DRI with high DRI quality, low carbon rate, and consequentially lo...

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The hot-wire type anemometers were used for measuring the velocity of effective air flowing through sinter bed in this study. Meanwhile, microphones were installed beside the pathway and close to the outer sidewall of travelling pallets for monitoring sound pressure generated by an abnormal air leakage. For identifying the passing pallet, a thermal-resistant type RFID technology was adopted. Based on the measured data via anemometers, the air leakage rate of sintering machine was calculated with the mass balance method, and pallets with the abnormal leakage can be detected and ranked in the severity of leakage from the measured sound pressure with the relevant criteria. In addition, for examining the leakage situation, this study set up a capillary type of differential pressure gauge to double cone valve (DCV) below the electrostatic precipitator (EP) in sintering plant for collecting the larger dust. The criteria of determining leaked DCV and the patterns for replacing the DCV were proposed to develop a detecting and predicting system on the air leakage into dust collectors of sinter machine. It offered field staff a basis of maintaining or renewing DCV via a warning reminding and reducing air leakage to increase EP efficiency for avoiding the dust emission from the stack. These technologies had been implemented in the sintering plants of China Steel Corporation, and they can effectively reduce the air leakage rate by 5% at least and further decrease the electricity consumption of the suction fan and coke rate, increase the production for the sintering machine.

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