Crane controls help make energy from waste
Olmsted County, Minn., has a waste-to-energy facility that burns nonrecyclable refuse to produce energy. To increase the amount of waste turned into usable energy, the facility underwent an expansion to increase its capacity from 200 tons to 400 tons of waste processed per day, with integration of updated drives, motors, and controls. The nearly $100 million project began in October 2007 and was completed in June 2011. Since opening in 1987, the Olmsted Waste-to-Energy Facility (OWEF) has processed more than 1.5 million tons of garbage into high-pressure steam and electrical energy used by nearby government buildings and sold to the power grid.
The existing plant had two 100-ton-per-day boilers. A 200-ton-per-day boiler was added during this expansion to increase capacity. Each boiler has a hopper that is fed waste by two 7.5-ton bridge cranes. With two boilers, the manual operation was an efficient method of moving refuse from the garbage pit to the loading hoppers. Now, with three boilers, the operation needed to vastly improve its efficiency to meet the project goal of doubled throughput.
Olmsted County hired Superior Crane to provide new trolleys, including new trolley and hoist motors, for each of the two waste handling grapple cranes. New semi-automated crane controls aimed to increase the cranes’ speed, reliability, and productivity. Superior Crane installed new variable frequency drives (VFDs) throughout the system, as well as a programmable logic controller (PLC) interface for each crane that allows the operator to pick a load of waste out of the storage pit and place it into one of the fuel loading hoppers. New arm chair control consoles were also incorporated for safe and convenient operator control of the cranes.
Two overhead bridge cranes are located 100 ft above the pit that is 21 ft deep, 50 ft wide, and 100 ft long, and holds up to 2,000 tons of refuse. Either crane can travel from one end of the pit to the other as the grapple descends to take bites of the stored waste to transfer combustible material from the storage pit to the loading hopper. The new semi-automated control allows the hoist, bridge, and trolley to effectively position the grapple over a specific, predefined area of the pit as requested by the crane operator. Once the load has been picked, the automated control system moves the hoist, bridge, and trolley as necessary to provide the most efficient path to the hopper.
The waste, after being loaded into the hopper, slowly travels 16 ft down onto the feed rams. The feed rams force the waste into the boilers. Ultrasonic monitors track the level in the hoppers and inform the operator when another load is needed. Each of the three fuel loading hoppers is fed alternately with the crane and grapple.
From the pulpit control station, 35 ft above the pit, an operator commands the semi-automated movement of the cranes and grapples from an operator’s chair communicating with a PLC in a central control room equipped to monitor and operate the facility. Two operator’s chairs exist, one for each crane. However, the system is designed to allow an operator at either chair to operate either crane on a first-come-first-served basis. Alternatively, two service stations are positioned on either end of the runway to allow manual control of the cranes for repair and maintenance.
The waste-to-energy facility’s efficiency and throughput were improved with two semi-automated bridge crane control systems using variable frequency drives, new hoist motors, and updated cab chair controls. The system also incorporates PLCs programmed to meet the project’s specific requirements. To ensure that the cranes operated per Olmsted’s specifications, VFD vendor system engineers performed on-site start-up services and training. As a result, Olmsted County increased the energy processed at its waste-to-energy facility by doubling the amount of refuse burned daily.
For the Olmsted County Waste-to-Energy Facility bridge crane project, the following automation products and services were used: variable speed drives (two models), PLC, hoist motors, cab chair console controls, engineering services, and application expertise. New retrofit control systems for two overhead bridge cranes were used to feed an additional furnace, doubling waste processing. New trolley-hoists increased crane performance. Updated drives, controllers, and motors ensured continuous operation. Semi-automated crane controls increased efficiency and reliability.
– Lynn Bostrom is director, communications, Magnetek. Edited by Mark T. Hoske, content manager, CFE Media, Control Engineering, firstname.lastname@example.org.
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