Batch heater plants

The process in this type of plant is different from that in a conventional batch plant. The plant is called batch heater because aggregates are dried and heated in batches prior to be mixed with the bitumen and filler. The dried and hot batch of aggregate is then dropped directly into the pugmill mixer, without being temporarily stored. 

Since there is no separation of the hot aggregate before mixing, the number of cold aggregate fractions used should be as many as possible (single-sized aggregates are used) to ensure consistency of the produced mixture. This increases the number of cold bins required. 

For all the above, batch heater plants are better suited for mixtures with low sand content, such as open-graded mixtures, which typically require low to medium mixing temperature. 

The total mixing time of a batch is almost 2 min and the typical hourly output ranges from 50 to 200 tonnes, depending on the model of the plant. 

The percentage of reclaimed asphalt incorporated in the mix, when using this type of mixing plant, cannot be more than 10% to 15%. 

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Consider a process worker monitoring a control panel in a batch processing plant. The worker is executing a series of routine operations such as opening and closing valves and turning on agitators and heaters. 

By far the largest number of the industrial freeze dryers in operation is of the vacuum batch type with freeze drying of the product in trays. There are two main types, depending on the type of condenser used. In the first type, the condenser plates are alongside the tray-heater assembly and in the same chamber in the second type the condenser is in a separate chamber joined to the first by a wide, in general, butterfly valve. This latter type of plant is always used in pharmaceutical industries, but it can also be used for the freeze drying of foods. Because of the wide variety and complexity of the... 

The dryer/heater of aggregates differs from the one used in batch plants in the following aspects (a) the burner is placed at the top end of the drum, (b) the configuration of the flights inside the drum is more complex and (c) the drum is longer. 

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