A new steam coil is hoisted and moved into the existing duct in the background.
Coal-fired power plants have special requirements for structural engineering services for regular plant maintenance, corrosion repair and emergency repair. Hanson regularly provides structural engineering services to these types of plants, which involve working with and without existing drawings and coordinating the numerous interferences that are generally present, which may not be indicated on available drawings.
A recent project at City, Water, Light and Power’s Dallman 4 unit in Springfield, Illinois, involved the design of monorail hoist beams to remove and replace steam coils from a duct in the plant. In the past, the plant had erected a temporary scaffold with monorails for maintenance work on the steam coils. The client requested permanent monorail beams to avoid the cost of setting up the scaffolding each time access to the coils is needed.
The steam coils in the duct are in two rows of four coils stacked on top of each other. The steam coils have a rigging point on each end of the coil for hoisting. They are hoisted by a monorail in the duct and transferred to a monorail outside to the duct. Two trollies are required to move each coil.
The elevation of new upper monorail beams had to be high enough to reach the top level of the steam coils, with enough room for a manual geared chain hoist and rigging. Two monorails with two trollies each had to be positioned to hoist the four rows of steam coils from within the duct. They were supported from the floor framing above the duct and attached to the framing with clamps to avoid welding or drilling into the steel. Clamping allowed the monorail beams to be installed by plant personnel and does not affect the existing framing capacity, other than the additional load of the framing and hoist.
Once the steam coils were pulled from the duct on the high monorail, they needed to be transferred to a lower monorail beam to clear a horizontal brace and utility framing that conflict with the full removal of the coils. Two trollies on the low monorail move the steam coils to a loading area, where they are taken out of the plant and replacement coils are brought in.
This type of work is typical for Hanson’s structural engineering services in power plants. Working around conflicts requires keen attention to the existing conditions. Once the conditions are understood, the solution to the client’s need can be designed.
For more information about these services, contact Ryne Fiorito at rfiorito@hanson-inc.com.
This image shows the new low monorail with trolleys and chain hoists. The new steam coil is below, at left.