Stick-built plants are said to offer the lowest cost to fabricate and ship to site. And stick-built construction is often chosen if the shipping of modules has to occur within a small window of favorable weather conditions, or because of local politics or labor constraints.
Despite these limitations, there is a growing trend in Engineering, Procurement and Construction (EPC) to provide modular components for combined cycle plants as opposed to the traditional stick-built approach. Many EPCs, such as Fluor Corporation, Gemma Power Systems, Vogt Power and Samsung C&T, as well as big OEMs, such as GE and Siemens, are leaning more towards modularizing some aspects of combined cycle facilities, i.e., the preconstruction of complete systems away from the job site that are then transported to the site. “EPCs can provide modules which are a better economic investment than stick building something onsite,” said David Dunning, Group President for Business Development and Strategy at Fluor.
Gemma Power Systems employed modular construction at a recent project near Palm Springs, California, consisting of several LMS100 aeroderivative turbines. “We would have needed to conduct thousands of feet of welding for a very large exhaust system in a very windy environment,” said Thomas Mastronarde, Project Engineering Manager at Gemma Power Systems. “Our modules used a bolted assembly so no welding was required.”
Other modular advantages include design standardization, ease of testing, faster project delivery and reduction of onsite labor. Siemens also favors modular or “standardized” construction, but cautions that any effort to implement a cookie cutter approach to the entire design of a power plant would be challenging due to the immense variability in climate, market forces, politics, geography and preference.
Siemens began on the modular path in 2003 with a design for a modular pipe rack. “We had to build a pipe rack on time, on site in Florida after a hurricane when there were no workers available and we ended up paying a premium for labor,” said Juergen Diekmann, the company’s power plant designer. “After that, we saw the value of modularization as it reduces the cost and time of construction.”
To date, the company has produced 10 pipe-rack modules. One such project, he said, moved 68,000 man hours off site. After the pipe-rack success, Siemens moved onto more modules for the air compressor, cooling skid, sampling container, fuel gas conditioning skid, raw water pump skid, fire pump house and demineralized water skid. As well as eliminating onsite labor, the benefits are said to include a reduction in scaffolding, painting, sandblasting and site congestion.
(You can read the rest of this article in the March April Edition of Turbomachinery International)