Adding the right mix
23 Feb 2005
With the increasing popularity of home breadmaking machines, it's tempting to think that just about anyone can bake the perfect loaf of bread.
And, after a bit of trial and error in getting the mix of ingredients just right, that might well be true — if it's just the one loaf you're after each time.
But move up to industrial scale baking and you are faced with the problems that beset all batch processors, whether the product is bread, beer, pharmaceuticals or any other commodity — that is, how to ensure that your process can deliver accurate and repeatable batches time after time.
One of the UK's leading bakeries has turned to Bürkert Fluid Control Systems to help it with just this problem. The company wanted a new automated dosing system designed to add minor fluid ingredients to its dough making processes at most of its UK sites.
Although some of the ingredients could have been added to the dough mixer in dry, solid form, automating the blending process was best achieved by dosing in all the ingredients in liquid form. From its initial brief, Bürkert project managed the design and installation of the fluid control system from concept to completion.
Bürkert's systems engineering manager, Paul Trevitt, was involved with the project from the start. 'We were given a list of the liquid ingredients by the bakery,' he says, 'complete with all relevant physical properties, such as viscosity and density, to enable us to design the flow control system to the required levels of accuracy.'
The actual ingredients remain confidential between Bürkert and the bakery, but each dosing system has been engineered to handle five individual streams, with space provided in the cabinet housing for an additional sixth ingredient stream if required later.
Each ingredient enters its relevant control line at the bottom of the cabinet and sequentially flows through, first, a manual isolation valve, then a flow meter, followed by a flow restriction/orifice plate, and then the process control valve itself. The accurately dosed ingredient then flows, via a three-way valve, out of the cabinet and on into the dough mixer.
All lines are 1in diameter stainless steel and, on four of the five, a positive displacement gearwheel type flowmeter is used. The nature of the ingredient being dosed through the other line, however, is such that a full-bore magnetic flowmeter was the preferred option here. The flow restriction plate provides a degree of flexibility in altering overall flow rates without having to respecify the system.
The flowmeters transmit pulse signals via the bakery's own Scada system to indicators on the front of the control cabinet. While each line could have been equipped with local control, it is in fact the Scada system that controls each process valve to open and close when required. The process valves are on-off, angle-seat, air-operated units controlled by pilot solenoid valves.
The flow rates handled by the system range from around 120 to 180 litre/h. But as dosing accuracy is so important to the bakery, the three-way valve on each line is used to switch the system into calibration mode. Also operated by the Scada system, these valves will divert flow from each line into a calibration vessel housed in the cabinet. Taking 2 litre samples at a time, this ensures the accuracy and repeatability of the system.
As Trevitt explains, what started out as a one-off order for seven units has now grown to an expected total of some 50 cabinets to be installed at various sites throughout the UK. A similar system has also now been sold to a pizza manufacturer and Bürkert received several serious enquiries from other bakery companies at last year's Total Process and Packaging show.
