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Phase 3: detailed engineering

The detailed-engineering phase of a project starts the 12 months typically required to design, fabricate, install, and commission a boiler. One way to begin this phase is with a diagram communicating the key requirements for both the water side and the fuel/combustion side of a solution. These requirements will drive the physical design of the solution and determine the size of the core components. Making these decisions early in a project is important to getting long-lead equipment items sized and on order. From there, piping and instrumentation diagrams can establish how a boiler will be controlled and operated and how steam, feedwater, and fuel systems will be integrated into the overall plant. Generally, Phase 3 is complete when the physical arrangement and plot plans for equipment, structural steel, and piping are finalized.

As important as keeping a project on time and on budget is ensuring that it is engineered efficiently and that the operations staff is engaged. Even the most elegantly engineered solution will break down if it is out of synch with the operating strategies and capabilities of the plant staff.

Phase 4: equipment and materials procurement and fabrication

The installation phase begins with site preparation and civil construction.

The procurement and fabrication phase runs concurrently with the detailed-engineering phase. To meet a 12-month project schedule, boilers, burner and controls packages, and forced-draft combustion-air fans must be ordered within weeks of the start of a project. Lead times for remaining components range from six to 20 weeks. To support an overall job schedule, equipment lead times must be matched to engineering time and drawing-review and approval time. The goal should be that virtually all equipment is delivered to the installation site during the first week of the installation phase (the first day of the eighth month of the 12-month design, fabrication, installation, and commissioning timeline).

Phase 5: Installation

Boilers can be set by crane or jacked into place.

The installation phase starts with site preparation and civil construction. Depending on the installation location, old equipment may need to be removed. At a minimum, robust foundations designed to support each piece of equipment must be built. This work should be completed two weeks before boilers arrive at a site and mechanical installation starts. Overall installation typically takes 16 weeks in a petrochemical-plant environment and a bit less time for a large commercial installation, such as a university campus or a hospital complex. Depending on their size, boilers will be delivered by truck, rail, or barge; almost always, they require specialized equipment and transport permits to be delivered and set on a foundation. From there, the economizer, SCR reactor house, stack, and interconnecting ductwork will be set. The burner might be installed in the field or at the boiler-fabrication shop. For larger boiler installations, fuel trains are skid-mounted, and forced-draft fans are set on their own foundations. If a boiler is a plant's first, water-treatment systems and feedwater controls will be set, and water, steam, and fuel piping will be run to connect the equipment on the boiler island and tie the solution into the plant. Mechanical installation will be complete once the system is hydrostatically tested. At that point, more-sensitive instruments can be mounted or installed, and insulation for thermal efficiency or personnel protection can be applied. The last part of this phase is completion of electrical wiring and instrument air tubing and the checking of loops for completeness and integrity.

Phase 6: start-up and commissioning

To ensure a smooth start-up, a qualified combustion engineer should be engaged before construction is complete. Start-up times can vary greatly, depending on the control schemes selected, the number of fuels to be burned, the emissions-control equipment included, and even the quality of the installation.