Optimisation of water flow

Description

Use of various control devices, e.g. photocells, flow valves, thermostatic valves, to adjust the water flow.

Technical description

Flow measurement and control techniques can reduce material waste and waste water generation in FDM processing. Applying flow measurement and control in transfer lines allows the accurate addition of materials to storage and processing vessels and filling packaging, thereby minimising the excessive use of materials and the formation of out-of-specification products.

Sensors such as photocells can be fitted to detect the presence of materials and to supply water only when it is required. Water supplies can be turned off automatically between products and during all production stoppages.

Valves are the most common control device and they are extensively used with both manual and automatic control systems. Valves are often used to modify a flow rate to control a different process parameter, e.g. the temperature of chocolate can be measured and, if necessary, adjusted by controlling the flow rates of heating and cooling water. Examples include flow regulators and solenoid valves; others are available.

Flow regulators are used to provide a constant flow at a predetermined rate. The flow through the regulator can be adjusted within a limited range, but these devices are designed with the intention that adjustments are infrequent.

Solenoid valves are two-position devices where a solenoid is used to open or close a valve on receipt of a control signal.

Food, Drink and Milk Industries 105

Table 2.42: Examples of the use of flow control in the FDM sector

Equipment Condition/activity Reason for control Transfer lines Accurate addition of materials to

reaction vessels

Minimise excessive use of materials and formation of out-of-specification products Steam supplies Maintaining correct operating

temperatures

Minimise waste from underheated or overheated materials and products Cleaning systems Water use Optimise use and minimise waste water

generation Source: [ 192, COM 2006 ]

Some typical applications of flow measurements are shown in Table 2.43.

Table 2.43: Typical applications of flow measurements in the FDM sector Product/activity Application

Soft drinks Flow measurement and feedback control for raw material addition

Bulk solids For example, determining the flow of potato crisps to a flavour drum to ensure the correct ratio of flavouring Milk powder Flow measurement for accurate batching of ingredients

into the process as specified in recipes

CIP Flow measurement to ensure a fixed volume of water issued for each cleaning stage

Source: [ 192, COM 2006 ]

Achieved environmental benefits

Reduced water consumption and associated energy use.

Environmental performance and operational data

An example food manufacturing company identified that excessive water consumption by its vacuum pumps was due to a higher flow than necessary for the seal water. Although the maximum flow for the service liquid should have been 2.7 m3/h, the actual flow was almost 11.5 m3/h, i.e. over four times the design requirement. Installing constant flow valves to ensure the correct flow rate to each of the water ring vacuum pumps reduced water use by approximately 60 000 m3/year, corresponding to 7.5 % of the site’s mains water consumption. Water and waste water costs fell and there was reduced energy consumption and wear of the vacuum pumps.

At an example chicken processing company, excessive water consumption was identified. Flow regulators were installed to fix the water supply to particular processes at the rate required by the process, thereby saving on water consumption.

An example fish processing company installed a solenoid system on the water supply to a prewash system. Water had previously flowed continuously, causing overflowing and entrainment of debris into the waste water. The solenoid enabled the water supply to be shut off when the conveyor belt was not in use. Water used by the process fell by 40 %.

In a brewery installation (#160), a vacuum is applied in bottles just before filling by a vacuum pump. Water flow is led into the pump to produce a venturi effect to take air out of the filler and also refrigerate the pump. There is a relationship between the vacuum generated by the pump and its working temperature, which is controlled by the cooling water. Using a thermostatic valve to adjust the raw water supply, it is possible to control the vacuum and save water. Water savings close to 0.1 hl/hl of products have been achieved [ 193, TWG 2015 ].

Cross-media effects

Technical considerations relevant to applicability

Flow regulators are widely applicable, where a constant flow is required at a set rate.

The use of solenoid valves is applicable throughout the FDM sector and they are frequently used to control water supply.

Economics

The introduction of constant flow valves in the food manufacturing installation referred to resulted in costs falling by GBP 70 000/year, giving a payback on the investment in less than one month.

At the chicken processing installation, the introduction of flow regulators cost less than GBP 1 000 and resulted in water savings worth over GBP 10 000/year.

At the fish processing installation, the 40 % reduction in water use saved GBP 2 500/year and gave a payback period of 5 weeks.

Driving force for implementation

Reduced water consumption and associated costs.

Example plants

Widely applied in the FDM sector.

Reference literature

[ 7, Environment Agency of England and Wales 2000 ], [ 10, Envirowise (UK) & Entec UK Ltd 1999 ], [ 192, COM 2006 ],[ 193, TWG 2015 ]