Energy Distribution

Power Efficiency Guide

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Energy is mainly supplied to the refinery in form of heat by burning of fuels and in the form of power either as electricity or steam as previously cited. Measures addressed so far rely basically on the operation of a simple unit, but some energy distribution through the diverse processes is also an opportunity for improvement.

Steam Steam can be used throughout the refinery, supplying energy for process heating, mechanical drives, enhanced separation processes, and can also be the water source for operations and chemical reactions. It can be generated by waste heat recovery from processes, cogeneration and boilers. Considering those three usual steam pressures available in a refinery, the highest one should be generated in a boiler or in a cogeneration system, which will be addressed in Chapter 10 . But the medium and lower pressures will be generated by waste heat recovery systems and steam turbines and these steam flows can be carried elsewhere in the complex for use. This is another recycling option.

Opportunities lie in the recovery of energy wastes of heating systems combustion flue gases, final cooling in heat exchanger trains, and even refrigerant water before its return to the cooling tower. They may provide low temperature or low grade heat but significant savings can be realized if they are in cascade and their heat recovered. Many high temperature furnaces have some heat recovery device to generate steam and this is another option for the distribution of thermal energy.

Efficient operation in this system is achieved by implementing actions like ensuring that the process has correct temperature control. Otherwise, instead of just reducing heat waste, it becomes a steam provider for the system, and that is not its purpose. Monitoring of the necessary process steam pressures and temperatures must be in place. Each process unit and equipment should have steam consumption standards and guidelines for regular adjustment of equipment depending on process changes, like throughput, campaign, temperature etc. General steam distribution awareness applies, like checking steam leaks, poor pipe insulation, faulty steam traps and providing their repair. Ensuring that as much condensate is returned from steam usage in the process is another step to be checked.

One particular operational feature is in generating proper amounts of low pressure steam through the use of back pressure steam turbines. This must be balanced all over the facility, matching steam and electrical power demand. Here a very important interface with electricity appears, where relevant savings can be obtained.

Electrical Power The task ofthe electrical power distribution system is to deliver the right amount of energy for the appropriate electrical equipment. The main uses of electricity are for heating, illumination and mechanical drive. Heating and illumination are usually very specific final consumption modes and although heat might be performed by other energy sources, when electricity is in use this normally means that other heat sources are not to applicable for some process reason. But mechanical driving builds an interconnection between diverse energy options inside a refinery.

Electric motors, gas and steam turbines can be used to drive pumping, compression and much other motive machinery. Choosing between them for each application depends on the availability of each energy form and its cost compared one to the other. But this apparently simple decision relies on the overall cost of the utility for the whole refinery. Just as an example, if in a refinery, high pressure steam is available and some process demands low pressure steam, using a turbine as a pressure reduction device while driving the fan or pump might be an economic option. But if that low pressure steam is in surplus, this choice might not be the best. Instead if the same operation can be performed by an electrical motor, using it could be better. And this equation also depends on whether electricity is generated on site, when usually it might be more efficient to use electric drivers. Constantly calculating and providing guidelines for choice between turbines and motors is a critical and sensible means of improving energy efficient operation of the electrical and steam distribution energy systems. And of course, complying with these guidelines and giving feedback about equipment availability is an important operational procedure.

Concerning electrical power planning and scheduling of large electric loads and equipment operations is another issue. An integrated approach for electrical load management demands reduction of energy usage peaks and a smoother, reliable and more energy efficient operation. Again some general care must be taken in electrical use , like reducing excessive illumination by switching, changing lamps etc; controlling lighting by awareness signs, use of daylight, skylights; or illumination devices with timers and presence sensors. When replacing electrical equipment either lamps or motors the use of higher efficiency ones should always be considered. Consider also the appropriate ambient temperature setting for air conditioning systems.

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