One of the largest fresh water consumers in a paper mill is the high-pressure cleaning showers used for paper machine fabrics. As the economics and environmental impacts of water use grow in importance, minimizing water consumption is a key objective. One often overlooked variable that has a large impact on water flow volume is the diameter of the orifice through which the water flows.
Two important factors determine the volume of water used: (1) the pressure at which the water is sprayed, and (2) the orifice diameter through which the water is forced. Flow through an orifice is proportional to the area of the orifice and the square root of the pressure as well as some friction factors that are dependent on the nozzle geometry.
Because flow volume depends on the area of the orifice, small changes in orifice size can have profound effects on that volume. The flow is proportional to the diameter of the orifice squared as illustrated in the following graph.Because the nozzle’s geometry changes as the nozzle wears, it is important to realize that nozzle wear adversely impacts water consumption. For example, consider a 200 psi shower system with 40 nozzles and a 0.040” diameter orifice. When the nozzles are new, the flow rate is about 25.1 gpm. If the nozzles wear just 5% to an opening of 0.042”, the flow increases to 27.7 gpm, an additional 2.6 gpm.
This increase in flow represents approximately 26,000 gallons of additional water consumption per week and over 1.3 million gallons every year (assuming 50 weeks of continuous operation). This additional consumption rate is for one shower system. A typical paper machine has an average of six high-pressure shower systems which equates to an additional 7.8 million gallons of water per year per machine. Justifying routine nozzle replacement becomes relatively easy considering the economics and environmental impact worn nozzles can have.
Replacing spray nozzles twice per year, in most applications, and selecting a nozzle material appropriate for the water quality and application will result in optimal water use in high-pressure shower systems.