HALLE, Germany (Aug. 22, 2013) – The problem is big.
An average of 39 million tons of sewage flow each year from the 35 most polluted combined sewer overflows (CSOs) in London—currently part of a 150-year-old Victorian network that can no longer accommodate the excess sewage and rainwater.
The challenges to solve the problem are even bigger—a pump station buried 85 meters below the surface in a shaft 32 meters in diameter.
At the heart of the solution are big pumps—54-ton Super Pumps specifically created by KSB to operate within a complex, carefully-engineered pumping system.
“This is the biggest wastewater pump that KSB has ever built,” said Maik Ulmschneider, head of KSB’s Waste Water Competency Center. “The whole project is superlative—the magnitude of the project itself, the size of the tunnel, the size of the pump, the size of the motor and the size of the test rig. The size makes it a challenge. Other than that, everything is normal. This is critical, innovative wastewater pump engineering, which is what KSB does best.”
Image 1. The Lee Tunnel pumping station shaft is as deep as Big Ben is tall.
The 7.6 kilometer (km) Lee Tunnel is the first of two tunnels designed to capture and redirect about 16 million tons of stormwater and sewage as part of the proposed 25-km Thames Tideway Scheme. It will run beneath the River Thames through Central London.
The depth of the shaft is equal to the height of Big Ben (see Image 1). The pumping station will operate below the Beckton Sewage Treatment Works, Britain’s largest wastewater and sewage treatment plant.
“This is the biggest water/wastewater infrastructure project in this decade in Europe,” Ulmschneider said. “Being part of this project is a big reference for us. We have gone above and beyond to find just the right customized solution that will make our customer happy.”
The investment for Thames Water is also big. The price tag of 2 billion pounds sterling for the entire Thames Tideway Scheme makes this the most expensive water project ever undertaken in the U.K.
KSB is providing the first four of the six single-stage, end-suction Super Pumps required to get the job done. It will also supply two smaller, but powerful, drainage pumps.
Each KSB SVP-84 Super Pump (cast and manufactured by GIW Industries in Grovetown, Ga.) will run in a working range between 3,050 liters per second (l/s)/87.1 meters of head (2.9 million gallons per hour (gph)/48,343 gallons per minute (gpm) and 1,950 l/s/16.89 meters of head (1.85 million gph/30,908 gpm).
The pumps feature impellers measuring 2.2 meters in diameter. Each wear-resistant, white cast-iron pump is powered by a Siemens A-modyn vertical motor, which runs at 3.4 megawatts (MW) at 6,600 volts/50 hertz and speeds up to 333 rpm (see “Powering the Pumps”).
To keep the motors cool, KSB designed heat exchangers specially engineered for this underground application. Compared with equivalent air-cooled systems, these heat exchangers will sharply reduce the amount of energy required to dissipate the thermal load.
“The biggest challenge in deep tunnel installations is getting as independent from the outside as you can,” Ulmschneider said. “Once any piece of equipment is hooked to the crane, it takes 20 minutes just to get it to the bottom of the tunnel. When you need to install several pieces, it can take a week to just get the equipment down there, and that doesn’t count the time needed to install it. The whole installation process in the shaft is a story in itself. The pump has to be installed inside the station. It is a very tight space. And of course, you can’t just call a guy and say, ‘I need help moving this 54-ton pump.’ It involves big, expensive equipment, a lot of people and a lot of time.”
KSB Halle's testing facility for the super pump. Click to enlarge.
Experience Solves Challenges
KSB has a history of successful applications in supplying equipment to similar scale projects in Russia, the U.S. and Mexico (see Pumps & Systems, March 2012 article “Wastewater Pump Stations Relieve Flooding”). This experience was essential in the company’s award of the contract.
“Deep installations come with many obvious challenges and other challenges that are found in the details during the design stages,” Ulmschneider said.
“We see a trend now that more big cities are using deep tunnels. One reason is increased awareness of the environment, so they think about CSO solutions. These solutions involve deep tunnels because all the other space in the ground is already occupied by metro, gas, normal sewage systems—all kinds of existing infrastructure.”
For the URS-422 project in St. Petersburg, Russia, KSB used smaller, dry-installed submersible pumps at a depth of 92 meters, Ulmschneider said. The best solution for this particular project was more pumps—12 of them—but the flow capacity of each pump was lower. “Because of this deep tunnel trend, we developed a complete range of pumps for both pure dry installation or dry-installed submersibles,” Ulmschneider said. “We expanded our existing range to meet the requirements of the trend.”
Each deep tunnel project requires a fully customized solution.