Chlorine processing throughput

It is estimated that the cost of treatment using MSO technology will be relatively high, due to high capital costs, labor requirements, and energy costs required to reach process temperatures. The cost per ton will be heavily dependent on process throughput and the chlorine content of the treated waste (D18091Q, pp. 9, 10). 

Gas recycle wastes energy and requires that the machinery be designed for more than the net process flow. The minimum practical amount of recycle is desirable from the standpoint of process efficiency. In chlorine processing, however, safety and process stability perhaps should be given more weight than in many other applications. Most systems have a constant recycle of up to 10% of throughput. 

On top of this, PVC is by no means the only chlorine source. Other raw materials and (particularly for blast furnaces close to the sea) even the air used in incineration processes may have significant contributions to the chlorine throughput too. 

With the Conrad process [1-3] a set of experimental runs with a throughput of approximately 100-1000 kg/h with PVC contents of up to 3% in a 60 20 20 HDPE PP PS base mixture have been performed. Typically 70-80% of liquids and 1-3% of solids are obtained. In scavenging the chlorine from evolving gases by hot calcium oxide and before condensation of the liquid fraction with a content of about 25 ppm chlorine were possible. Similar results were obtained by treating the plastics in the kiln with calcium oxide during pyrolysis. A direct condensation without any calcium oxide treatment led to concentrations of up to 10000 ppm chlorine. 

Throughput rate is the gallons of sludge fed to the unit per unit time (gpm or gpd). If the sludge is treated by chlorine (a disinfectant/oxidizing agent), the oxidized sludge is the chemical oxidation effluent. Chlorination is an oxidation process. 

The control system is automatic, with little operator attention required. There are three variables that affect operation. They are throughput rate, chlorine feed rate, and system pressure. The throughput rate has been designed for an expected solids concentration. The process chlorine feed is set based on the expected rate of solids fed to the oxidation unit. If the actual solids concentration increases, the throughput rate should be lowered. 

In a suction chiller, chlorine returned from liquefaction boils at compressor suction pressure. Since this pressure is usually close to atmospheric, chlorine will boil at about —34 C, where its heat of vaporization is 288 kJ kg . Returning 15% of the net throughput to the suction chiller can cool the gas to —30°C or lower and allow the compression ratio in the first stage to be increased by about 58%. This technique increases the flow of chlorine through the compressor by the amount of liquid vaporized. In cooling the gas, it removes no heat from the process. The heat load ultimately is transferred to the refrigeration system in liquefaction. 

This procedure is in the direct competition to the incineration plant for the PVC recovery. The process can recycle mixed plastics with a high PVC content, like that produced from building waste. LINDE-KCA DRESDEN GmbH (a subsidiary of LINDE AG) offers a plant of this type with throughput rates of up to 8 t/h. The plant may also be operated efficiently as a stand-alone plant for small quantities of waste. It recovers the chlorine in the form of aqueous HCl directly during depolymerisation. 

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