Recoup lost energy dollars in your foundry's compressed air system.By examining your compressed air compressed air, air whose volume has been decreased by the application of pressure. Air is compressed by various devices, including the simple hand pump and the reciprocating, rotary, centrifugal, and axial-flow compressors. system for pressure and moisture problems, you may be able to reduce energy waste by as much as 70%. Because the market demands it, foundrymen are always searching for ways to cut costs without cutting quality or performance. Many of these cost reductions are the result of testing new products, re-engineering casting processes, pushing the capabilities of molding machinery, or rethinking planned wage increases. But there are also substantial gains that can be made without gambling with your proven metalcasting processes. Namely, you can make great strides in reducing costs just by taking a good look at your compressed air system. WASTING AIR MEANS WASTING ENERGY Compressed air is the most expensive utility, costing nine times as much as electricity, and it's the second highest consumer of electricity in many foundries. While it's typical for compressed air systems to waste about 50% of their total operating cost, foundry installations often waste 60-70% because foundries tend to be older and contain a fairly hostile maintenance environment. In addition, air lances and blowoff Blowoff A term in technical analysis that refers to a sharp price increase that comes after a long period of price appreciation, and is followed by a fall in the price. A blowoff is seen as a rally's last breath and is a highly bearish sign. devices are manually operated and exhaust high volumes of uncontrolled air. Production consistency, uptime and low scrap generation are often dependent on the compressed air supply that supports the equipment. Advanced systems that include PLC and computer-controlled equipment are cost-effective if they can produce high-quality cores and molds at cycle rates that exceed traditional methods. In many foundries, traditional methodology often coexists with this leading-edge technology, and both are linked to a common air system. As a result, manually controlled points of use, such as air lances, can have a profound effect on more sensitive equipment like robotic handlers handlers persons involved in the handling of, for example, circus animals. Includes grooms, milkers, herdsmen, strappers. Used mostly in referring to persons handling animals for show or auction. or stackers. It's not unusual to experience long and tedious new equipment commissioning due to air inconsistencies. Compressed air users should strive to: * create an energy balance between supply and demand; * establish operating standards governing flow, pressure and consumed power; * set physical design standards Design standards Specifications of materials, physical measurements, processes, performance of products, and characteristics of services rendered. Design standards may be established by individual manufacturers, trade associations, and national or governing compressors, dryers, filters, piping and controls; * institute point-of-use practice standards governing how air is used; * develop instrumentation standards that generate performance and diagnostic data; * base actions and decisions regarding compressed air on technology - not assumptions. Understanding Your System The collection of piping and equipment in your air system can be intimidating in·tim·i·date tr.v. in·tim·i·dat·ed, in·tim·i·dat·ing, in·tim·i·dates 1. To make timid; fill with fear. 2. To coerce or inhibit by or as if by threats. , but armed with a knowledge of the fundamentals, you can better understand your own setup. The basic compressed air system consists of an air flow generator that mechanically works against a back pressure (compressor compressor, machine that decreases the volume of air or other gas by the application of pressure. Compressor types range from the simple hand pump and the piston-equipped compressor used to inflate tires to machines that use a rotating, bladed element to achieve ), which is connected to a pipe system. Flow will increase or decrease depending on the pressure in the pipe and the size of the production demand and leakage. If leaks are repaired, the pressure in the pipe will tend to rise, increasing the flow through the remaining open holes. As air pressure in the pipe increases, so does the flow and air velocity, which in turn increases air loss and destabilizes pressure. Adding compressors creates the need for more power. Storage creation and pressure stability allow you to develop a totally managed system [ILLUSTRATION FOR FIGURE 1 OMITTED]. In order to translate repaired leaks to reduced consumption, use primary storage, which is generally installed near compressor stations, to stabilize the pressure inside the pipe so that it remains constant, regardless of the hole size. The signature of an unmanaged system is the attempt to manufacture compressed air and deliver it where it is needed instantaneously. This requires that excessive energy be used just to drive air at high velocities through the pipe, exaggerating pressure changes in the pipe - exactly what we are trying to avoid. Storage is defined as receiver tanks or the piping itself in which the outflow is controlled to a lower pressure than the supply. In creating storage, the system's distribution pressure downstream of storage can be reduced. This lower, constant pressure throughout the system will reduce flow through the holes, which in turn reduces compressor horsepower. A Managed Air System An esoteric definition of air management is the ability to control the expansion of compressed air from generation to points of use. Two common misperceptions that tend to govern the points of use are: * all compressed air points of use need as much pressure as can be supplied; * if there is a problem at the points of use, it is caused by low air pressure. This approach fails to take into account information on the pressure level itself. Often, the present pressure level is unknown due to broken or, for that matter, any pressure gauge pressure gauge Instrument for measuring the condition of a fluid (liquid or gas) that is specified by the force the fluid would apply, when at rest, to a unit area, such as pounds per square inch (psi) or pascals (Pa). at the use point. If the only working pressure gauge is located at the air compressor, it's impossible to know if you have low or high air pressure where you need it. It's essential to understand the interdependency between the decisions made at the point of use and how those decisions affect the rest of the system. To determine your optimal system configuration and reduce losses: * determine your required translation pressure (the applied combination of flow delivered at pressure that translates into mechanical work); * establish a standard that limits the dynamic pressure drop between the supply header and the point of use. Determine the actual dynamic translation pressure by connecting a calibrated cal·i·brate tr.v. cal·i·brat·ed, cal·i·brat·ing, cal·i·brates 1. To check, adjust, or determine by comparison with a standard (the graduations of a quantitative measuring instrument): gauge to the use point itself. If the static pressure is 90 psi (gauge) and the dynamic pressure is 60 psi (gauge) with tile use point in operation, the dynamic pressure drop is 30 psi (dynamic), an excessive amount. This drop should not exceed 5 psi (dynamic). In this example, 30 psi (dynamic) amounts to an additional 20% energy requirement, which must be made up by the compressor. In some situations, the dynamic translation pressure may be higher than the desired distribution pressures. In this case, install situational air-powered booster compressors. Another way to optimize your system is through eliminating surges. A surge presents high flow rates for short durations to the distribution system. Surge demands characterize certain types of connected loads such as pulsed dust collectors and bin vents. If surges are untreated, they tend to divert the air supply from other demands that display a higher impedance to flow, such as in air motors that power a drilling station. This results in the perception that the distribution pressure is low. The best way to isolate surge is to provide additional storage (secondary), which is generally located adjacent to the demand. In addition to receiver volume and discharge regulation, a metering valve must be installed to the receiver at the inlet. This valve serves as a gate to retard air flow into the receiver. A dust collector will typically activate based on a repeat cycle timer or on the pressure differential in the fan stream. Either method will establish a dwell time The time cargo remains in a terminal's in-transit storage area while awaiting shipment by clearance transportation. See also storage. between cycles. For example, if the dwell time is 20 sec, storage pressure restoration can be delayed to 16 sec. This dampens the surge effect and prevents transitory TRANSITORY. That which lasts but a short time, as transitory facts that which may be laid in different places, as a transitory action. periods of high-velocity air flow in the piping. Auditing the System You can go about developing and implementing an air management program in several ways. An independent auditor Independent Auditor An external auditor with a certified public accounting designation that qualifies him or her to provide an auditor's report. Notes: These auditors aren't affiliated with the company being audited. can develop a program based on an extensive sight review combining an empirical study with data gathered by logging pressures, flows and kW consumed. The report should reveal characteristics and concerns relative to your system as it currently exists as well as a performance model that shows what you could achieve through reconfiguration. In addition, the report should provide the required economic data for reconfiguration to help management make decisions based on its viability, return on investment and productivity gains. Proper system analysis often can lead to strategies that will reduce energy consumption by 20-30%. A foundry also can implement several steps to contribute to the goal of a managed system. 1. Install calibrated pressure gauges at the compressor discharge: discharge of air treatment, dryers and filters; distribution piping; and points of use, including the manifold of a dust collector. 2. Add regulation or set existing regulators based on the readings from the gauges. 3. Begin a leak detection and repair program employing an ultrasonic ultrasonic /ul·tra·son·ic/ (-son´ik) beyond the upper limit of perception by the human ear; relating to sound waves having a frequency of more than 20,000 Hz. ul·tra·son·ic adj. 1. gun. Fittings, couplings and components that are discovered to be repeat leak points should be replaced by better parts. 4. Attempt to find alternative motor power sources such as low-pressure sand conveying and venturi-based atmospheric nozzles for abusive demands. 5. Plan primary and secondary storage, surge stations and pressure boosters. By taking the first steps, you can relate proactively with a consultant to expedite the project and ensure your involvement in the entire reconfiguration process. Every successful program requires an in-house lead person who can communicate ideas .between production, plant engineering, maintenance and management. THE WATER PROBLEM Another aspect of efficient air management is the need for a dry system. The first question asked by virtually all companies using compressed air is "why is it important to dry the air?" The following are just a few of the reasons: * moisture in instrument air systems fouls delicate moving parts Moving parts are the components of a device that undergo continuous or frequent motion, most commonly rotation. "Parts" only include the mechanical components which does not include fuel, or any other gas or liquid. ; * water washes off the lubricant Lubricant A gas, liquid, or solid used to prevent contact of parts in relative motion, and thereby reduce friction and wear. In many machines, cooling by the lubricant is equally important. in pneumatic tools pneumatic tool (n  măt`ĭk), instrument activated by air pressure. Pneumatic tools are designed around three basic devices: the air cylinder, the vane motor, and the sprayer. , leading to premature wear; * when molten metal comes in contact with compressed air, any liquid moisture or oil in the air can be disastrous, leading to serious injury, or death; * in cold climates, where the temperature may fall below 32F (0C), the pipe or other components may freeze due to the moisture in the system; * moisture in compressed air piping leads to corrosion, and flakes of rust can be carried downstream by the compressed air into some of the valves and cylinders, blocking critical orifices. Sources of Moisture The next question typically asked is "where does the water in my compressed air system come from, and how do I get rid of it?" All atmospheric air contains some moisture, or relative humidity relative humidity n. The ratio of the amount of water vapor in the air at a specific temperature to the maximum amount that the air could hold at that temperature, expressed as a percentage. . Compressing the air causes the air to become very hot, and when this air cools down to a specific temperature, free moisture, or condensate condensate, matter in the form of a gas of atoms, molecules, or elementary particles that have been so chilled that their motion is virtually halted and as a consequence they lose their separate identities and merge into a single entity. , is released into the air stream. Temperature Considerations The air's ability to contain moisture is based mostly on its temperature, so, as the hot discharge air is cooled in the compressor after-cooler, the discharge air temperature approaches the cooling media temperature (either water or air), and moisture begins to condense con·dense v. con·densed, con·dens·ing, con·dens·es v.tr. 1. To reduce the volume or compass of. 2. To make more concise; abridge or shorten. 3. Physics a. . The air leaving the after-cooler/moisture separator is now at a new dewpoint (the point at which the air is 100% saturated). In other words Adv. 1. in other words - otherwise stated; "in other words, we are broke" put differently , any additional drop in the compressed air's temperature would result in liquid moisture. Drying the System The after-cooler is the most common type of air dryer An air dryer is a device that is mounted directly after an air compressor and dries the air. Compressed air is kept in pressure vessels, mostly made out of steel. Wet air will corode the pressure vessels inside and rust in a pressure vessel may contaminate the pneumatic system so found in most compressed air applications. An aircooled after-cooler, however, is not 100% efficient in reducing the temperature of the compressed air to the ambient temperature Outside temperature at any given altitude, preferably expressed in degrees centigrade. . Water is a better cooling media than air, therefore, the approach temperature of a water-cooled after-cooler is often better. The other advantage of water as a cooling medium is the stability of the temperature of cooling water throughout the year. A coalescing coalescing (kō  les´ing),n a joining or fusing of parts. type of filter is required to remove the oil and water vapor from the compressed air. Other Dryers Once this filter is in place, you must determine what degree of dryness is required by the process. The three basic dryer types are absorption, condensation and adsorption adsorption, adhesion of the molecules of liquids, gases, and dissolved substances to the surfaces of solids, as opposed to absorption, in which the molecules actually enter the absorbing medium (see adhesion and cohesion). dryers. The characteristics of each type of dryer varies, and your choice of which dryer to use depends on the application. 1. Absorption (Deliquescent del·i·quesce intr.v. del·i·quesced, del·i·quesc·ing, del·i·quesc·es 1. a. To melt away. b. To disappear as if by melting. 2. Type) * Advantages - Lowest initial cost and no moving parts. * Disadvantages - Dewpoint suppression from 15-20F (-9.4 - 6.6c); prefilter is required to protect media; media must be added or replaced; downtime The time during which a computer is not functioning due to hardware, operating system or application program failure. to change media; disposal problems and costs; high operating costs operating costs npl → gastos mpl operacionales vs. CFM dried; carryover of media downstream; and bed can solidify so·lid·i·fy v. so·lid·i·fied, so·lid·i·fy·ing, so·lid·i·fies v.tr. 1. To make solid, compact, or hard. 2. To make strong or united. v.intr. causing channeling. 2. Condensation (Refrigeration refrigeration, process for drawing heat from substances to lower their temperature, often for purposes of preservation. Refrigeration in its modern, portable form also depends on insulating materials that are thin yet effective. Type) * Advantages - Constant dewpoint of 38F (3.3C); low maintenance costs; no recurring costs except power; no after-filter required; lowest operating cost/CFM; non-cycling operation, longer compressor life; and always removes, never adds contaminants to the air. * Disadvantages - Lowest-possible dewpoint is 38F (3.3C). 3. Adsorption (Desiccant desiccant /des·ic·cant/ (des´i-kant) 1. promoting dryness. 2. an agent that promotes dryness. des·ic·cant n. Type) * Advantages - Lowest pressure dewpoint available to 100F (-73.3C). * Disadvantages - Highest initial cost; pre and after filter required; periodic desiccant replacement; highest cost of drying/CFM; and inlet air temperature limited. There also are a variety of "point of use" dryers which are available to handle special circumstances special circumstances n. in criminal cases, particularly homicides, actions of the accused or the situation under which the crime was committed for which state statutes allow or require imposition of a more severe punishment. . This article was adapted from a presentation at the 1998 Northwest Regional. RELATED ARTICLE: Achieving a Real Energy Reduction A northeastern malleable iron (Metal.) iron sufficiently pure or soft to be capable of extension under the hammer; also, specif., a kind of iron produced by removing a portion of the carbon or other impurities from cast iron, rendering it less brittle, and to some extent malleable. foundry was looking for Looking for In the context of general equities, this describing a buy interest in which a dealer is asked to offer stock, often involving a capital commitment. Antithesis of in touch with. a way to reduce its electrical demand peaks, and by examining its compressed air system, was able to fix problems, increase the efficiency of its equipment and achieve annual savings of more than $80,000. The 123-worker, green sand shop had equipment dating back to the 1920s, and little had been spent on capital improvements over the years. The foundry's compressed air system was composed of one 250-hp reciprocating, one 200-hp rotary screw and one 75 hp reciprocating compressor A reciprocating compressor is a compressor that uses pistons driven by a crankshaft to deliver gases at high pressure.[1] [2] The intake gas enters the suction manifold, then flows into the compression cylinder where it gets compressed by a piston , as well as one 600-gal receiver. No air dryers were installed to combat moisture in the system. The major points of use in the system included a dense phase handling system for sand transfer, two pulse-type dust collectors, actuators on the facility's heat treat oven doors, about 12 air-powered grinders, several 1-in. air lances used to cool ladles, several open blowdowns to exhaust water and an air-powered stacker using rodless cylinders. Four pressure recording data loggers data logger - data logging were set up to measure maximum air pressure and determine the difference in pressure gradients In atmospheric sciences (meteorology, climatology and related fields), the pressure gradient (typically of air, more generally of any fluid) is a physical quantity that describes in which direction and at what rate the pressure changes the most rapidly around a particular location. throughout the system. Several days of on-site analysis revealed that while all three compressors were in operation, the distribution pressure in the system was 86-118 psig. There was leakage of 40% and uncontrolled demand of 50%, and normal operation resulted in an operating cost, power only, of $186,923/year. The piping system was adequate to handle the demand, but every air demand was creating the need for high-velocity instantaneous delivery because there was no storage. In addition, parts of the system demonstrated abnormally low pressure because the dust collectors created higher pressure gradients in that section of the piping system. Stackers would shut down on a low pressure alarm as a result. The remedy was to install a 4000-gal receiver (storage) and intermediate flow controller adjacent to the compressors, a 600-gal surge station supplying the dust collector, and a 600-gal receiver supplying the dense phase handling system with a 21 air amplifier to supply seal and actuator A mechanism that causes a device to be turned on or off, adjusted or moved. The motor and mechanism that moves the head assembly on a disk drive or an arm of a robot is called an actuator. See access arm. air. Also, a 400-gal secondary storage receiver was installed upstream of the stackers, and air lances were regulated to 50 psi. Distribution pressure at intermediate controls was reduced to 80 psig [+ or -]2 lb, and a refrigerating re·frig·er·ate tr.v. re·frig·er·at·ed, re·frig·er·at·ing, re·frig·er·ates 1. To cool or chill (a substance). 2. To preserve (food) by chilling. air dryer was added to the system so that the multitude of open drains Open drain is one of the many different electrical input/output standards in digital designs today. Definition The word "drain" in the term "Open-drain" refers to the drain terminal of a MOSFET transistor. (The analogous term for BJT devices is open collector. could permanently be closed. Before any changes were made, pressure fluctuations were causing the stackers to fail, and the dense phase sand handling system would often become overloaded. Lost production time due to these problems was about 12%, but once the facility implemented changes, it was able to eliminate lost production time attributed to the air system. The project cost $140,000 (including the capital expenditure, rigging rigging, the wires, ropes, and chains employed to support and operate the masts, yards, booms, and sails of a vessel. Standing rigging is semipermanent, consisting mainly of mast supports, the fore-and-aft stays, and the stays running from the masthead to each side and installation), but the facility saw a return on its investment in 21 months. The revised power cost for the system fell to $106,813 - a projected annual savings, power only, of $80,110. RELATED ARTICLE: A Sample of Air Leakage Costs The following is just an indication of the cost of your air leaks and should motivate their repair. This sidebar illustrates how much money could be slipping through your fingers (in ballpark numbers and assuming a constant distribution of pressure). If you have a 100-hp compressor, you can assume that the capacity will be about 4 cfm/installed hp, or 400 cfm at 100 psi (gauge). The average plant loses about 20-30% of their compressed air capacity to air leaks. This would equate to 80-120 cfm at 100 psig in this example. Assume that the plant operates on a 2-shift, 16-hr day, five days/week, and 48 weeks/year. This would add up to 3840 hr/year. Assume that your power cost would be $0.05/kWh. Therefore: 80 cfm [divided by] 4 cfm/hp = 20 hp 20 hp x .746 = 14.9 kW 14.9 kW x 3840 hr x $0.05 = $2,860.80/year This is equivalent to a leak of just under 0.25 in. 120 cfm [divided by] 4 cfm/hp = 30 hp 30 hp x .745 = 22.35 kW 22.35 kW x 3840 hr x $0.05 = $4,291.20/year This is equivalent to a leak of just over 0.25 in. Multiply the above percentages based on your actual compressor hp to determine how much you're wasting. |
|
||||||||||||||||||||
Printer friendly
Cite/link
Email
Feedback
Reader Opinion