US experts jet into Morupule B blame-storm

Lawrence Seretse | Friday March 21, 2014 15:53

And, the key parties at Morupule B – the Botswana Power Corporation and Chinese contractor, CNEEC – are already sparring over culpability for the boiler-related faults that have caused widespread economic losses from prolonged load-shedding and supply uncertainties.

This week, Mmegi established that while the US firm has been contracted to conduct an independent root cause analysis, the BPC says its own probe points to discrepancies between designers and manufacturers of the key components.“We summoned the designers and manufacturers of the boilers and heat exchangers to site after noting frequent failures with the same components,” BPC CEO, Jacob Raleru told Mmegi on the sidelines of a media briefing.

“What was found was a difference between the design and what was built.

“The designers came up with a conceptual design and took it to the manufacturers, before the contractor installed it.

“The installation itself, by the contractor, was done according to the specs, but things fell between the cracks between the designer and manufacturer.”

While Raleru’s statement seems to exonerate CNEEC who installed components in the power station, the Chinese firm is not off the hook. As the Engineering, Procurement and Construction (EPC) contractor, CNEEC sub-contracted the designers and manufacturers.

“The designers were sub-contracted to CNEEC; they were engaged by the contractor,” he said.“We know CNEEC and our contract is with them. CNEEC’s contracts with the designer are back-to-back arrangements..”

Raleru added that the designers’ analysis of the problems at Morupule B could not be taken as gospel due to the nature of the sub-contracting relationship with CNEEC.

“The root cause analysis will be independent because the designers are sub-contractors to the contractor and they are possibly interested parties,” he said.

CNEEC officials however deny responsibility for the troubles with the boilers and heat exchangers, saying that initially they had expressed their dissatisfaction on the use of the Fluidised Bed Heat Exchanger (FBHE) boilers by Doosan Letjes GmbH, a German company that was drawn in to design the plant boilers. They said it was an outdated boiler model.

CNEEC counter blames that they had advised government to choose the Circulating Fluidised Bed boilers (CFB), which was less complex and widely used according to international standards, but BPC would not budge.

CNEEC asserts that at BPC ultimately no one was fully aware of the design defects that were to surface at the use of the FBHE boilers.

“BPC could not make any technical decisions. Fichtner approved the use of that FBHE boiler design at the time even though we informed them that it is not used in China and we had never used it before,” a senior source at CNEEC revealed. “BPC opted to believe Fichtner. We disagree about a lot of things but if BPC instructs us we end up doing something even if we know its wrong. However, none of us was fully aware that a complication of this nature could arise, we just know that CFB is the best.” 

 

The boiler blunder

Mmegi’s investigations into the defects that the boilers is said to be faced with, drew into the picture what the engineer at Morupule B described as a boiler design blunder.

The engineer disclosed that the FBHE approach includes a fluidisation chamber, into which hot solids are introduced, usually from the solids separator.

Heat transfer tubes are located inside the fluidised solids, and thus the heat transfer rates are higher than in conventional gas channel super heaters. Simultaneously, the solids entering the chamber contain only low amounts of corrosive substances.  “This leads to lower material loss rates than in other super heater types,” he points out.

However, the continuous erosion by the fluidised particles and the high thermal load set special needs for the materials that are used in the tubes. At the same time, the demand for higher steam parameters and increasingly difficult fuels set additional demands to the proper selection of steels.

“New supercritical steam parameters create demands for creep strength up to 750°C temperatures. Such steels that can handle so high temperatures are rare, and if the environment is corrosive, risks of too high material loss rates have to be taken into account in the plant design,” the engineer explained what lead to boiler explosions.

Currently, the best means of protecting heat transfer surfaces from erosion-corrosion is the re-modification of the boiler designs. 

The engineer explained that tubes in a fluidised bed heat exchanger have to be selected according to the “worst case” scenario of steam temperature + 100°C, there are only few applicable materials. He said every time the boiler explodes at Morupule B, the high temperature fluids get mixed with the coolers, the bed ash and limestone mixture, the whole boiler remains clogged in concrete.

“By the time the boiler cools down for us to gain access, the whole surface area would be covered with solidified cement.

Now you can imagine trying to revive the boiler at such conditions, its a month’s job,” he said.

In this case CNEEC mentions that the designers gave them a solution on how to re-modify the boiler.

The solution entailed cutting out the two heat exchange tubes.  Unit 2 and 3 had undergone this process last year and Fichtner is yet to approve before BPC can take them over.

 

Time for some western expertise?

Mmegi understands the US firm engaged by the BPC has “extensive experience in building power station using boiler technology similar to Morupule B”.

The results of the root cause analysis will enable government and the BPC to trigger recourse clauses in the contracts surrounding Morupule B’s development. Already, the BPC and government have the cover of a two-year “defect notification” clause which places CNEEC under liability for any faults at the power station.

“The defect notification period lasts for two years and kicks off after the hand-over of the last unit,” BPC sources said. “At present, Unit 2 still has not been handed over.”

CNEEC officials recently said the Chinese firm had thus far lost about P300 million due to the delays in Morupule B’s completion. 

“The project has been delayed for about 18 months now and we have incurred out of budget costs of over P20 million a month,” one official said.

“We will not make any money on this project, In fact we are going to make a huge loss. But our president has said that despite the losses we should make sure we deliver the project and bring it to completion. Energy minister, Kitso Mokaila has also revealed that government held Morupule B’s performance bond “and everything we need for the plant”.

“We have also not paid out all the money (for the contract),” Mokaila told business leaders recently.

While CNEEC is expected to bear the brunt of the root cause analysis’ findings, any one of the numerous contract parties to the P11.1 billion project could be caught in the spotlight.

Contractual players in Morupule B include government, the BPC and its various consultants as well as CNEEC and its various sub-contractors. A new player, STEAG, entered the scene in January as the BPC’s new Operations and Maintenance contractor for the power station, after CNEEC’s unceremonious exit.

The US firm is also expected to investigate the root cause of high noise levels within the plant.