Cobden, Vic, Australia
Sinclair Knight Merz was engaged to develop and design an air mixing device for the Cobden Milk Factory. To produce milk powder, a fine spray of concentrated milk liquid is mixed with hot air in a large drying chamber. At the milk factory, the hot air is produced by a gas fired gas-to-air tubular heat exchanger. A temperature mal-distribution exists at the outlet from the air heater, varying from 120oC to 240oC from one side of the duct to the other. This mal-distribution produced uneven drying conditions and the loss of dryer capacity due to the loss of the heat in the exhaust air.
Sinclair Knight Merz provided a design solution that would produce a more uniform temperature distribution without increasing the pressure loss that would limit the capacity of the drying system. The firm was able to apply its knowledge of the equipment used in pulverised fuel (PF) distribution systems to design the device.
The device directs a portion of the colder air across the duct to the hotter side and a portion of the hotter gas to the colder side. The streams of different temperature air then mix naturally in the 20 m of inlet duct to the dryer. Facilities were provided so that the quantity of air transferred across the duct could be adjusted to optimise the downstream temperature distribution. The challenge was to achieve the required mixing with minimal pressure loss.
The device provides the required uniformity of temperature without requiring any tuning/adjustment and an improvement in capacity was achieved due to the lower pressure loss through the device compared with the previously installed mixing baffle plates. The client is now able to include such a device as part of any new plant, providing a competitive advantage.