When Grupo Secacao looked to expand its Guatemalan hydropower base by building a new station on the Choloma River, it faced a serious challenge in terms of how it would transport water over the mountainous countryside. Steel pipe was the norm, but the difficulties of the terrain and the exacting standards needed to properly fit steel pipe sections together made the project owners look for another solution. Grupo Secacao choose high-density polyethylene pipe — a more flexible material that would adapt better to the area's rugged conditions. This solution has the 21 MW Choloma plant up and running, providing electricity to Guatemala's power grid.
Grupo Secacao, a group of companies based in a tropical region in northeastern Guatemala, owns and operates three hydroelectric plants on its 3,000 hectare property. Previously, the property functioned as a coffee farm, but analysis of the land showed it was suitable as an area for hydroelectric power generation. There are several water sources on the property, mainly the Secampana, Secampanita, Golondrias, Caquipec and Choloma rivers. The first plant began operating in 1998 and has an installed capacity of 16.5 MW. The second plant, which began operating in 2006, is downstream of the first plant and has a capacity of 4.6 MW.
Recently, Grupo Secacao added a third hydroelectric plant, 9.7 MW Choloma, which uses water from the above mentioned rivers. Water is conveyed via a 6 km-long low-pressure pipeline to a steel holding tank. From the tank, a 3 km-long high-pressure pipeline conveys the water to the powerhouse, which is located 460 metres below the tank, thus providing the high head for the Pelton turbine installed in the powerhouse.
|High-density polyethylene pipe was used to supply water to the 9.7 MW Choloma powerhouse in a hilly part of Guatemala because of its flexibility over uneven terrain and its lower installation costs when compared with stainless steel pipe.|
All the plants feed the country's main power grid and together, the three can potentially provide about 1.5% of Guatemalan electricity demand.
The three plants are about 8 km apart in a remote part of Guatemala within the Santa Cruz Mountains. Access to the Choloma site during construction involved helicopter rides and long and complex logistics for transport of containers and cargo. Planning ahead and ensuring the correct materials were sent to the site was a top priority.
In addition to generating power using a sustainable resource, maintaining a healthy ecosystem and supporting local communities are also very important to Grupo Secacao. The company maintains a sustainable environment around the three hydroelectric plants, protecting the land, environment and watersheds. On 700 of the 3,000 hectares, the company planted new trees and reforested areas. In addition, Grupo Secacao has a conservation program in place on 500 hectares of the land, which consists of a tropical rainforest that includes a variety of plants and wildlife.
Community programs have included support for local schools, the construction and operation of a community health center with a maternity and emergencies clinic, and the development and construction of nine community-wide rural electrification projects that brought electricity for the first time to about 500 families.
Why HDPE pipe?
Parts of the Choloma water conveying system require only a low-pressure piping system. The pipeline terrain from the rivers has many hills and curves. Steel pipe, which Grupo Secacao had used at the other two facilities, would require a significant number of exact fittings and numerous welds, taking about 25% more time and involving several design challenges to accommodate the rolling landscape.
Because using steel pipe was more costly and presented significant challenges, Grupo Secacao decided to look into other potential piping materials, one of which was HDPE. Another alternative was fiberglass pipe. However, fiberglass pipe is not fused but mechanically joined together. Mechanical joints presented some installation and safety concerns, as it is not a monolithic system when joined, presenting the potential for leaks and requiring longer installation time. Fiberglass pipe is also more rigid than HDPE pipe.
Because Grupo Secacao had not used HDPE pipe before, representatives of the company met with ISCO Industries of Louisville, Kentucky, USA, a global pipe supplier and manufacturer of HDPE products, to learn more about HDPE pipe for low-pressure applications. ISCO personnel took Grupo Secacao's Vice President and Executive Director Rudolf Jacobs and General Manager Rodrigo Tormo on a tour of a project in Oregon in the USA to show them the benefits of HDPE pipe and its potential for use at the Choloma project. A few days later, the same ISCO personnel traveled to Guatemala to visit Choloma, do a walkthrough of the pipeline system, and assist in details related to an HDPE pipe system.
Jacobs and Tormo were pleased with what they saw and learned from the visit to this project. "We have a very positive impression of HDPE pipe," Jacobs says. "Generally, many hydro plants here have some form of a low-pressure pipe collection system. Historically, we have used steel pipe for this application, but steel pipe has complications. It's a lot more difficult and expensive to install in the field. It's slower to install because the trenching needs to be a lot more exact and there are many more welds to complete. Weather in the rainy season provides a great challenge to the welding process of steel pipe."
"HDPE pipe is basically a giant garden hose. It's very flexible and works extremely well. The weld station remains stationary for longer periods of time, covering a high number of welds of the pipe sections that are ‘pulled through' the welding machine, saving time and allowing work in challenging weather conditions. The benefits of HDPE pipe come during installation, from the reduction in installation costs," he added.
In the fall of 2010, the group contracted with ISCO to supply about 2,438 metres of 91 cm-diameter pipe, 3,048 metres of 122 cm-diameter pipe, nearly 1,524 metres of 45.7 cm-diameter pipe and some 60.7 cm-diameter pipe.
In addition, ISCO provided several fittings, valves, flange adapters, fusion equipment rentals and three onsite field technicians to fuse pipe and provide fusion instruction to the crew.
ISCO began supplying materials for the low-pressure water conveyance application in December 2010. The pipeline was designed to follow an existing winding gravel road. Once the pipe was situated along this road, Grupo Secacao personnel started to fuse the HDPE pipe with help from ISCO.
The fusion and installation of the HDPE pipe began from several strategic positions that had been predefined and worked backwards toward the various water sources. Six intake structures were constructed at each of the water sources, designed so that the flow from these streams would collect in the 45.7 to 122 cm-diameter pipeline running across the slope. Initially, the pipe was fused above ground and later placed in a trench, covered and compacted. The HDPE pipe was fused and installed along the landscape, connecting river intakes and intersections, and running along the hills and curves of the area.
The fusion machines were on site for nearly eight months until all fusions were completed. In total, 8 km of pipe were fused. Fusion times varied based on weather conditions, location and other factors. The area experienced heavy rains and some landslides, but the fusions still occurred in a timely manner.
A large steel water tank was constructed on a ridge near the Choloma River at an elevation of about 647 metres. It is 61 metres in diameter and 10.7 metres tall and has about 20,000 m3 of live storage. The completed low-pressure water conveyance pipeline was connected to this steel holding tank.
For the high-pressure pipeline, a 106.7 cm-diameter steel pipeline (2,950 metres long) was connected on the other end of the holding tank. It carries water down a steep slope from the steel tank to the powerhouse. The steel pipe was used for this application because it required a higher pressure rating due to the steep slope.
Using HDPE pipe for the low-pressure pipe saved time and cost on the project. Fewer welds were required with the HDPE pipe because of HDPE pipe's flexibility and bend radius. The cost savings from HDPE came from a reduction in installation costs because of the fusion process and the flexibility of the pipe. The actual product-to-product cost comparison between steel and HDPE pipe is similar.
Grupo Secacao successfully completed the pressure test on the pipe, and the system began operating in early October 2011. The completed project is running well, with positive impacts to the region's environment and society. Because the Choloma plant uses a renewable resource, it does not produce any carbon dioxide or other pollution during generation. Grupo Secacao has applied for certification of the project under the Clean Development Mechanism of the United Nations Framework Convention on Climate Change, intended to help reduce global warming.
— By Joanna Climer, public relations specialist, ISCO Industries, and Rudolf Jacobs, vice president, Grupo Secacao