Epasa Breakthrough Transforms Heavy Fuel Oil Sludge into Resource Stream

Brazilian independent power generator Epasa faced significant environmental and operational challenges with heavy fuel oil sludge. Through innovative engineering and problem-solving, the company developed a state-of-the-art two-stage de-watering and de-oiling process that transforms sludge into reusable resources.

For nearly a decade after Centrais Elétricas de Paraíba—or Epasa—began commercial operation of its Termonordeste and Termoparaíba plants in 2010, the Brazilian independent power producer grappled with the dual responsibilities of providing thermal power for reliability while addressing its shareholders’ environmental concerns. The two power plants near João Pessoa, a dynamic coastal city on Brazil’s eastern tip, contribute a combined capacity of 342 MW, making them together the second-largest fuel oil thermoelectric complex in Brazil and among the top five largest in the world. As Epasa Plant Manager Marcelo Agra Junior explained to POWER, the facilities are equipped with 40 engines from MAN Energy Solutions, including 38 MAN/STX 18V32/40 motors with a generating capacity of 8.76 MW each and 02 MAN/STX 9L32/40 motor capable of 4.38 MW. EPASA utilizes OCB1, a low-sulfur content heavy fuel oil, to fuel its operations. 

While Brazil now relies on renewables—mainly hydropower—for 80% of its generation capacity, the plants play a pivotal role as a standby resource when reservoir levels at Brazil’s hydropower facilities are low, Agra said. However, the thermoelectric’s environmental posture has come under sharp relief in recent years, owing partly to a societal embrace of decarbonization and a sustainability push by Epasa’s two shareholders—CPFL Energia, Brazil’s second-largest transmission and distribution company, and EBRAZIL, a thermoelectric power giant in Brazil. “So, we focus a lot on mitigating our environmental impact as much as possible, [mainly] by mitigating our productive process and our impacts on the local community,” he said.

For years, Epasa’s most significant environmental impacts came from ensuring its HFO was adequately purified, a step essential to protect and extend the life of its engines. Impurities in HFO can lead to significant wear and tear, operational inefficiencies, and even failures. To purify its raw HFO, Epasa had used centrifugal separators manufactured by German firm GEA and Swedish company Alfa Laval. Centrifugal separators purify HFO by rapidly rotating the oil to generate centrifugal force, separating the denser impurities and water from the oil, efficiently clarifying the oil for use in engines and generators.

Centrifugal separators, however, produce sludge, a concentrated mass that is often composed of separated impurities and water, which gets entrapped with the solid particles during the separation process. At Epasa, which uses 1,600 tonnes of HFO daily when it is generating at total capacity, sludge beneficiation had quickly grown into an imperative.

“Normally, our sludge composition is 80% of water and 20% of oil,” Agra explained. Before, Epasa would truck out the sludge to a third party for treatment, with the recovered oil going to industry, he said.

“So, imagine the quantity of trucks that we needed to send this sludge—which is mainly water—to a third party to treat.” Agra noted that the practice was both expensive and environmentally averse.

Treating Sludge In-House

In 2019, Epasa’s internal engineering departments proposed an ambitious solution to treat the sludge in-house. “The pillars that we envisioned were to use the sludge as much as possible in our process, to treat the water in compliance with the Brazilian environmental legislation, and then to ensure, through 24/7 supervision, to treat the water, abiding by legislative limits so that we could return it to rivers.”

However, after researching solutions by visiting sludge treatment facilities globally, Epasa realized the solution did not exist as a commercial offering. The company then moved to contract a Brazilian engineering company to help it design a dedicated system that would cater to the power plant’s specific demands. “The complete system would have required integrating technologies from two vendors,” Agra noted.

1. Epasa’s system featured a GEA OSE 80 for sludge beneficiation and the WSE 20 bilge separator for purifying oily water before disposal. Courtesy: Epasa

Following engineering discussions, which lasted more than a year, Epasa convened an in-house group of experts and collaborated with GEA, which “opened a window to change specific components in their standard equipment” and adapt the project to Epasa’s needs. Under the working solution, Epasa purchased a GEA OSE 80 centrifugal separator to beneficiate the sludge produced by the standard GEA and Alfa centrifugal separators during the purification of raw HFO. In addition, Epasa integrated a GEA WSE 20 bilge separator to purify the oily water before disposal (Figure 1).

Essentially, as Agra explained, the system operates in two key stages. In the first stage, the GEA OSE 80 centrifugal separator, with an effective capacity of up to 2,300 liters per hour and operating at a separating temperature of 95C, beneficiates the sludge. This de-watering process efficiently separates the sludge into three distinct outputs: water, which still contains oil ranging from 5% to 30% by volume; treated oil that Epasa could reuse as fuel; and sludge residue, suitable for direct delivery to industrial users such as cement and ceramic industries. The initial mixture entering the OSE 80 typically comprises 70% to 95% water and about 3% solid content, highlighting its capacity to handle high moisture content effectively.

The second stage involves the GEA WSE 20 centrifugal separator, designed to process up to 1,200 liters per hour at a slightly lower temperature of 90C, which focuses on de-oiling. This stage is crucial for treating the oil-laden water produced in the first stage through a combination of filtration, coalescence, and separation techniques. At this stage, the mixture predominantly consists of water (99.8% by volume) with a minimal oil content of 0.1%. This ensures that the final discharged water meets environmental standards for disposal or potential reuse in other processes.

2. Epasa’s sludge beneficiation system is the first worldwide to implement a complete GEA Group system in a thermoelectric power plant, utilizing centrifugal separators for sludge beneficiation and water purification. Courtesy: Epasa

The project, implemented in 2021 (Figure 2), immediately showed promising outcomes, but after an extensive period of monitoring and operating the treatment system, Epasa’s team identified an opportunity to make improvements. “Initially, the project aimed to obtain beneficiated sludge with low moisture content to be commercialized with added value,” the company noted. “However, the product obtained from treating the HFO sludge by the GEA OSE 80 separator had a water content well below 1%, and laboratory tests showed that the product met HFO specifications. Thus, whenever the product was compatible with the fuel stored in the storage tank, we directed the beneficiated sludge for burning in our engines, thereby reducing HFO consumption.”

A Meaningful Project with More Potential

According to Agra, the project has so far helped Epasa reduce its HFO losses from 2% to 0.2%. That alone has shown some economic gains. “The payback of the project could be less than three years, though that would require full generation for three years, which is not our reality,” he said. In addition, the system is attractive, given that installation of the system was relatively straightforward, he noted.

A short-lived challenge he highlighted was that the system’s integration into the plant required a temporary halt to operations. After that, implementing the solution efficiently requires time to adequately train plant personnel and ensure that they can integrate the new process into existing operations, he said.

For Agra, a more significant lesson rests in the experience it gained in pulling together various experts to resolve a longstanding problem. He suggested that the solution now stands as a lucrative business opportunity for Epasa.

—Sonal Patel is a POWER senior editor (@sonalcpatel, @POWERmagazine).