Energy Optimization of Hydraulic Systems : An investigation of energy-efficient designs for hydraulic systems

Abstract: An investigation of the global energy consumption debate confirms the complexity of the global environmental issues, the severity of the impact in developing countries and the major efforts that is required to discourse this development. Electricity production is the largest growing source of CO2- emissions, mainly due to the expansion of coal power plants in China and India. Therefore one can easily argue for the importance of develop more environmentally friendly use of coal. However, the cheapest measure to reduce CO2-emissions is not to develop new technologies but to use the produced energy more effective, regardless of energy source.  In this final thesis in mechanical engineering investigates the possibilities of modifying two hydraulic systems in an energy efficiency perspective. The investigations will show if there is potential for implementing energy-saving investments in hydraulic systems. Two hydraulic units that are representative for the hydraulics at Sandvik Materials Technology were chosen. One unit controls a hydraulic system that moves steel bars through an oven, and the other unit drives machines that straighten crooked tubes. Pressure-measurements and calculated flow demands showed that both systems had potential for energy efficiency work. By the use of accumulators four different concepts have been developed. With an investment analysis as a basis, one concept per system has been considered profitable.  For the system referred to as the tube-straightener a concept that uses two pumps and motors of two different sizes has been considered profitable. The thought is to let the smaller pump and motor take the base-load of 2 kW that is used when the motor is idle-running. A timer shuts the machine after 25 seconds, which is where the profitability of the concept is found. Hence, large energy consumption savings can be achieved just by changing the time set on the timer. With the modifications that are represented in this thesis, the energy consumption is decreased by 45 %.The potential for energy efficiency work is thereby confirmed. However, the analyzed systems are too small to generate a short pay-back time. If similar modifications are performed on larger units, the pay-back time will drop dramatically.  In the most economic viable concept for the hydraulic system referred to as the oven, one of the existing three pumps is removed. The two remaining pumps control two different flow different demands. One pump manages the flow demand of one cylinder with a high demand. The other pump manages the remaining flow demand with the help of installed accumulators. The motors are replaced since the current motors are oversized. This investment has a payback period of 2.7 years and will reduce the energy consumption by 25% which corresponds to approximately SEK 25 000. Furthermore, the eyes are lifted from the specific systems that have been subjected to this analysis and underlying factors of over dimensioned hydraulic systems in today´s industries are brought up. Incentives that affect the constructor’s decisions play an important part in the underlying factors that is presented. As long as the constructor is punished to a greater extent for undersized systems than he or she is rewarded for designing smaller, more energy efficient systems, this problem will remain. Another aspect that is brought up is the time limit, when the time limit is set very short the risk of losing precision in estimation of needed system capacity increases.