As promised in my previous blog that introduced the topic of energy management, I will delve further into the topics areas mentioned. This one concerns Energy in Manufacturing
Energy in Manufacturing
It is up to industry to do something about energy efficiency & reduction before governments start legislating targets to individual industries & companies.
The first area that people think about when energy efficiency is talked about is manufacturing. In fact the EPA recognizes manufacturing plants for Energy Efficiency with its ENERGY STAR program and published Energy Efficiency Guidelines for the following industries: Breweries, Cement Manufacturing, Corn refining, Food Processing, Glass Manufacturing, Motor Vehicle Manufacturing, Petroleum Refining, and Pharmaceutical Manufacturing http://www.energystar.gov/index.cfm?c=in_focus.bus_industries_focus
Petrochemical Processing is a focus industry but the guidelines have not been published to-date (April 2008).
If fact the U.S. government expects that energy intensity in most manufacturing sectors to decrease in the future. Each company must do their part in decreasing energy usage in manufacturing.
Each system in your facility or facilities should be examined for inefficiencies. Comparisons between like equipment and systems can give an indication that inefficiencies exist. Continual monitoring of equipment and systems energy efficiencies can lead to identifying problem areas in maintenance, production scheduling, or investment. Benchmarking against the manufacturer, industry, and your own internal standards can lead to identify problem areas where equipment and systems are not performing effectively.
For example: Steam Generation Efficiency
Steam systems offer many opportunities for improvement. Some examples are:
Reduce deaerator flow vent to <.1% water flow or <.5% steam flow, lower steam header pressure if there are no turbines, check boiler / vaporizer efficiency regularly, select fan speed for ambient conditions, install adjustable fan blades.
Further examples can be found in CIBO Energy Efficiency Handbook – Council of Industrial Boiler Owners 1997
An effective way to assess the efficiency of your steam system is to benchmark the fuel costs in dollars per 1000 pounds of steam. The cost is dependant on fuel type, unit fuel cost, boiler efficiency, feed water temperature, and steam pressure.
- Source: Energy Tips Steam, – Steam Tip Sheet #15 January 2006 – U.S. Department of Energy – Industrial Technologies Program Energy Efficiency and Renewable Energy
Water is essential for steam generation. Properly conditioning water can increase the efficiency of a boiler. Without proper treatment server problems can develop some of which can be so sever that the boiler itself could be destroyed. Proper conditioning helps to ensure safe and reliable operations.
Most boiler water problems fall into two areas: deposit related and corrosion related.. It is very common for these to areas to be interrelated. One of the most common problems is boiler scale build up, which happens when some of the common elements (calcium, magnesium, and silica) found in water react with the tube metals in the boilers form a hard scale. This scale reduces the heat transfer and consequently reduces the boilers efficiency. In the worst case the accumulating scale can cause the tubes to overheat and rupture.
Silica scale is similar to boiler scale. Silica is found in most water supplies and is not as easily removed form the water supply as the components of boiler scale
Internal treatment of boiler water involves the removal of impurities in the water as discussed above. Comment methods to remove the impurities include lime softening, sodium cycle citation exchange, reverse osmosis, electrodialysis, and iron exchange demineralization. The treatment that is needed, depends upon the composition of the water supply, its quality, and the purity requirements of the boiler.
In a clarifier, adding quick lime to hard water, for example, reacts with the calcium, magnesium, and to extent with silica to form a participate. This “treated” water is now softer that the non treated water but is still not suitable for a boiler. This softening treatment is followed by either sodium cycle citation exchange or ion exchange demineralization. Citation exchange is usually used for low pressure boilers (450 psig and demineralization for high pressure boilers (above 600 psig). Iron exchange is a process that exchanges one type of iron for another. Many impurities in water are irons. Iron exchange takes place in a closed vessel which is partially filed with an iron exchange resin. Another method of iron exchange is sodium exchange softener, where the hard water enters the exchange and the calcium and magnesium are exchanged for sodium.. This method is only good for low pressure boilers. If very pure water is require by the boiler specification then demineralization is required. Here water is treated in two steps, cations are exchanged for hydrogen ions. This results in water that is free of citations but is too acidic. This acidic water now has to pass through an anion exchange bed where the anions are changed for hydroxide ions. The hydrogen ions and the hydroxide react to form water, which is now suitable for using in the boiler
- CIBO Energy Efficiency Handbook – Council of Industrial Boiler Makers
Part of the investigation should be to see if it is possible to reduce unnecessary steam flow. By reducing the steam header pressure in their steam system, Nalco Chemical Company was able to save $142,000 annually and reduce annual energy consumption by 56,900 million Btu. The project did not require a capital investment and there was minimal downtime involved. The amount of energy used was reduced by 8% per pound of product. Additionally by operating at lower flow velocities and energy levels the steam systems experience lower levels of erosion and valve wear.
- Source: Office of Industrial Technologies Energy Efficiency and Renewable Energy – U.S. Department of Energy
For Example: Steam Traps
In a steam system which has not been maintained for 3 – 5 years, between 15 – 30 % of the installed steam traps may have failed, thus allowing live steam to escape. In properly maintained systems leaking traps should account for less than 5% of the traps. Just repairing steam leaks can save 1 – 2 % in energy. Rohm & Hass projected an annual savings of $50,000 by improving the steam system maintenance in its Knoxville plant.
· Source: Chemicals Best Practices Plant Wide Assessment Case Study Industrial Technologies Program – Energy Efficiency and Renewable Energy U.S. Department of Energy DOE/GO-102003-1714
By identifying and repairing all problematic steam traps Dow Chemical Company saved $881,000 and 112,128 MMBtu at their St Charles’ plant.
- Source: Energy Use and Energy Intensity of the U.S. Chemical Industry Ernst Worrell, Dian Phylipsen, Dan Einstein, and Nathan Martin – Energy Analysis Department Environmental Technologies Division Ernest Orlando Lawrence Berkley National Laboratory University of California LBNL-44314
Velesicol Chemical Corporation Maryland facility implemented a maintenance program that identified energy losses in their steam system and saved over $80,000 annually, saved 27,308 million Btu annually, reduced annual CO2 emissions by 2,400 tons, reduced annual consumption of treatment chemicals by 1,000 pounds, saving over $20,000 per year, decreased worker exposure to treatment chemicals, and reduced make-up water use by 56%
- Source: Chemicals: A Steam System Technical Case Study – Office of Industrial Technologies Energy Efficiency and Renewable Energy U.S. Department of Energy
For a steam system to operate efficiently, the steam traps must remove condensate as it forms without releasing steam. There are a wide range of designs and sizes for a variety of manufactures. However there is no universal design for all applications. Selecting the appropriate & maintaining steam trap is critical for system performance.
Steam traps have multiple modes of failure. The two that are most noticeable are a) failure closed – passing no condensate or steam and b) filed open – passing live steam. If a trap is failed closed, condensate will back up into the system. A heat exchanger with failed closed steam trap will allow heat transfer to take place. This type of failure will generally be discovered since the process component will not be performing correctly or at all. A failed open steam trap can potentially pass a significant amount of steam, which becomes an energy loss to the system..
Determining that a steam trap is operating properly can be a difficult task, especially with system that has a closed condensate return systems, that is, a system where the trap discharges into a pipeline system. Here visual inspection is quite difficult as the trap is not usually visually accessible.
There are four primary ways of testing that a steam trap is operating properly: temperature, sound, visual, and electronic.
Temperature analysis of steam trap operation investigates the approximate temperature of the fluid entering & exiting the steam trap To utilize this method the steam trap must be understood an the operating pressures, and the degree of sub cooling must be known.. Additionally different types of traps will operate under different temperature constraints.
Sound monitoring of steam traps is an investigation method that incorporates listening to the trap in operation. This can be accomplished through sonic or ultra sonic methods Evaluating the condition of the steam trap based on its audio profile is complicated and must take into account background noise and the similarity of live steam and flash steam passing thought the trap
Visual inspection techniques observe the steam trap output. Sometimes the capability to observe the discharge of the system is not built in. So other methods have to be used. For visual inspect to be successful the inspector must be familiar with the discharge conditions of all the traps they encounter. A gross failure is relatively easy to identify, but given the volume flow of flash steam it is difficult to identify between a properly operating trap and one that has failed.
In general steam trap inspection requires multiple methods of inspection. Identification of gross problems is normally easier that minor failures. The time & expertise required to properly inspect steam traps has cause manufactures of steam traps to develop monitoring components for their products. These components come in two forms. One is a sensor that is fitted to the steam trap that continually monitors the steam traps operation, the other uses a portable device which determines the acoustic & thermal signal of the trap and compares it to a database of acoustic and thermal signals of a properly operating steam trap of identical type and model.
Source: Steam System Survey Guide – Greg Harrell, Ph D., P.E. May 2002
Oak Ridge National Laboratory
Recommended test intervals:
- High Pressure (150 psgi and above) weekly to monthly
- Medium Pressure (30 to 150 psgi) monthly to quarterly
- Low pressure (below 30 psgi) annually
- Source: Steam Tip Sheet Number 1 U.S. Department of Energy
For Example: Pump System Efficiency
It is possible for a pumps efficiency to degrade as much as 10 – 25% before it is replaced and efficiencies of 50 – 60 %. However these inefficiencies are not readily apparent and opportunities to save energy by repairing or replacing components are often overlooked.
Pumping System Efficiency (nsys) is defined as follows
nsys = Qreq x Hreq x SG / 5308 x Pe
Qreq = required fluid flow rate, in gallon per minute
Hreq = required pumphead in feet
SG = specific gravity
Pe = electrical power input
For further information see ANSI / HI 1.6-2000 Centrifugal Pump Test and ANSI 2.6 – 2000 Vertical Pump Test
In the U.S. , more than 2.4 million pumps consume more than 142 Billion kWh annually are used for industrial manufacturing purposes. At an electrical cost of 5 cents per kWh, energy used for fluid transport costs more than $7.1 Billion per year. A continuously operated center fugal pump driven by a fully loaded 100 hp motor required 726,000 kWh per year. Using 5 cents per kWh this cost more $36,000. Thus even a 10% reduction in operating cost results in savings of $3,600 per year.
Inefficient system operation can be cause by a number of problems; poor pump selection, bad design of the system, excessive wear on the components, cavitation, and wasteful flow control practices.. Indications of an inefficient system include; high energy costs, excessive noise in the pipes and across valves, and high maintenance requirements.
A key to improving system performance & efficiency is to fully understand the system requirements (peak demand, average demand, and the variability of demand) throughout the year. It is easier to design a system that operates with relatively constant load requirement than one that has to account for large variations of demand.
In order to compensate for these peaks most systems have oversized pumps. The problems with oversized pumps is that excessive energy is used operate them when not at peak. Many operators do not understand the impact of running a system at higher than required pressure and flows. Pumps and value line ups are usually set up to handle the worst case but are not truly set for the normal (lower)l loads. This causes unnecessary wear on the components of the system. Unfortunately, having over sized pumps increases the cost of operating & maintaining the system and creates a series of operating problems.
This over sizing also applies to the control values in the system. The valves are oversized to ensure adequate flow in the face of the unknowns of pump performance, pipeline fouling, scaling, and future production rates. Consequently most control vales normally operate at less than 50% open. These highly throttled control values impact the control loops. Major contributors to process variability are control vale backlash, and static friction. The proper sizing of the pump and control valves provide a more uniformed response to flow changes and reduces process variability.
· Source: Improving Pump Performance – A Sourcebook for Industry – U.S. Department of Energy October 2006
On a further note; for the U.S. operators, a framework on certifying industrial plants for energy management has been proposed by a collaboration of industry, government, and non-profit organizations to improve the energy intensity of U.S. manufacturing by 25% by 2017 http://www.superiorenergyperformance.net/. In addition the US Department of Energy offers assistance to companies in increasing the effectiveness of their plants through the SAVE ENERGY NOW program. This is done by carrying out assessments focused primarily on energy intensive systems. On average, each large plant assessment yields potential savings of $2.5 million. You can apply for an assessment via http://www1.eere.energy.gov/industry/saveenergynow/assessments.html