PLANT REPORT: ECOELECTRICA LP – Sidebars 1 thru 8

1. Talented, empowered staff the force behind EcoElectrica’s success

EcoElectrica’s primary business objective is to provide reliable, flexible, and efficient energy production and tolling services while excelling in safety, environmental preservation, regulatory compliance, and community relations. These words are not window-dressing: They are the personal goals of the dedicated employees who make this electric generating facility in Penuelas, PR, world-class.

Day-to-day leadership of EcoElectrica is provided by co-general managers: Carlos A Reyes, PE, for operations; Jaime Sanabria for finance and administration. They report to a Board of Directors representing the three owners: GDF Suez, Mitsui & Co Ltd, and Gas Natural Fenosa.

The facility is staffed by 78 employees, the majority assigned to O&M of the power block, desalination plant, and LNG terminal (chart).

Approximately 90% of EcoElectrica’s personnel are “locals,” living within about 30 minutes of the plant. One-third of the employees have Bachelor’s degrees, 10% Master’s degrees, and one a Doctorate. This is highly unusual in the power generation business today. Several first-line managers also are licensed professional engineers as the O&M org chart attests.

SB 1

 

2. LNG backgrounder

SB 2Liquefied natural gas is odorless, colorless, non-corrosive, and non-toxic. When vaporized and mixed with air, it burns only in concentrations of 5% to 15%. Neither LNG, nor its vapor, can explode in an unconfined open environment, according to information provided by CH-IV International, a unit of MPR Associates Inc, Alexandria, Va. CH-IV provides engineering services related to the design and operation of LNG facilities.

Natural gas is composed primarily of methane, but may also contain ethane, propane, and heavier hydrocarbons. Small quantities of nitrogen, oxygen, carbon dioxide, sulfur compounds, and water also may be found in pipeline natural gas, but they are removed during liquefaction.

LNG usually is referred to as light or heavy depending on its methane content, which ranges from about 82% (heavy) to 99% (light) depending on the source and type of processing. The methane fraction for a typical shipment received by EcoElectrica from its primary supplier, Atlantic LNG Co of Trinidad, is in the neighborhood of 96%. The table presents the range of LNG compositions used in the design of the EcoElectrica terminal.

The composition of LNG changes during tanker transport because some of it evaporates. The more volatile methane evaporates faster than the heavier hydrocarbon components, thereby increasing the gross calorific value of the fuel. Effects of ageing should be considered by the user prior to delivery, especially if a long voyage is involved.

LNG tanks always are of double-wall construction with an efficient insulation system between the walls. Large tanks (EcoElectrica’s is 42-million gal) are cylindrical in design and have a domed roof; they are characterized by a low ratio of height to diameter. Storage pressures in these tanks are low—less than 5 psig, according to CH-IV engineers. LNG must be maintained cold— below about minus 180F—to remain a liquid, independent of pressure.

Small tanks, those having a capacity of 70,000 gal or less, generally are horizontal or vertical vacuum-jacketed pressure vessels. Range of design pressures for these containers extends from less than 5 to more than 250 psig.

The insulation, as efficient as it may be, will not keep the LNG reservoir in its liquid state. CH-IV experts explain that LNG is stored as a “boiling cryogen”—that is, as a very cold liquid at its boiling point for the storage pressure maintained. They suggest thinking of stored LNG as analogous to boiling water—only 470 deg F colder. The temperature of an open pot of boiling water does not change, even when more heat is applied, because it is cooled by evaporation.

In much the same way, the experts continue, LNG will remain at near constant temperature if maintained at constant pressure—a phenomenon called “auto-refrigeration.” As long as the LNG boil-off gas (BOG as it is called) is allowed to leave the storage tank, the temperature remains constant. If BOG were not removed, then the pressure inside the tank would rise. Example: At 100 psig, LNG temperature would be minus 200F. However, the cost of building a 1-million-bbl pressure vessel for LNG storage would be prohibitively expensive.

Safety. No discussion on the handling and storage of any fuel is complete without a thorough review of safety history, procedures, and best practices. The most serious US accident involving LNG occurred in Cleveland in 1944 before the behavior of cryogenic liquids in storage was well understood. The space program contributed significantly to the collective knowledge on cryogenics and post-Cleveland there have been only two safety incidents related to domestic LNG facilities, according to CH-IV research:

  • A construction accident on Staten Island 40 years ago that has been cited by some as an LNG accident because it involved work inside an empty and warm storage tank.
  • The failure of an electrical seal on an LNG pump in 1979 permitted natural gas to enter an enclosed building and a spark of indeterminate origin caused an explosion. Revisions to the electrical code since that time would prevent such an accident from occurring today.

CH-IV International offers a detailed history of accidents at LNG facilities onshore and offshore worldwide on its website at www.ch.iv.com. In addition, and perhaps more importantly, its experts discuss the mechanics of gas explosions—including the vaporization of LNG spills and the mixing of the resulting vapor with air, ignition sources, and ignition of an LNG vapor cloud.

 

3. Regulatory oversight focuses on safety, environmental protection

Integrating an LNG terminal with a powerplant significantly increases the number of regulations and permits governing facility design and operation compared to those required for a standalone combined cycle. Plus, with more federal and local agencies involved, there’s greater regulatory oversight of facility operations to assure compliance with the additional rules.

Here’s a list of the regulatory agencies monitoring activities at EcoElectrica and what their responsibilities are:

Federal agencies

Federal Energy Regulatory Commission (FERC) approval is required for the siting of new onshore LNG facilities. The Energy Policy Act of 2005 designates FERC as the “lead agency for the purposes of coordinating all federal authorizations” and the agency responsible for complying with federal requirements under the National Environmental Policy Act of 1969.

FERC also is responsible for monitoring the safety and security of operating LNG facilities on an ongoing basis, coordinating its efforts with the US Coast Guard (USCG) and the Dept of Transportation (DOT). While DOT and FERC have agreed that the former has exclusive authority to promulgate federal safety standards for LNG facilities, the latter can issue more stringent safety requirements when it believes they are warranted.

The agency monitors LNG terminal activities in accordance with 18CFR153, “Applications for Authorization to Construct, Operate, or Modify Facilities Used for the Export or Import of Natural Gas”; 18CFR380, “Regulations Implementing the National Environmental Policy Act”; and NFPA 59A, “Standard for the Production, Storage, and Handling of LNG.”

Compliance involves semiannual reporting and an annual audit.

Dept of Homeland Security (DHS)/ US Coast Guard (USCG) assure facility security compliance in accordance with 33CFR101, “Maritime Security: General”; 33CFR105, “Maritime Security: Facilities”; and 33CFR127, “Waterfront Facilities Handling LNG.” The USCG acts as a cooperating agency in the evaluation of LNG terminal applications and has the authority to review, approve, and verify plans for marine traffic around proposed onshore LNG terminals as part of the overall siting approval process led by FERC.

Annual inspections of security and maritime operations are conducted according to the requirements of the Maritime Transportation Security Act. Inspections also are conducted of each LNG unloading operation.

Environmental Protection Agency (EPA) assures compliance with air emissions in accordance with provisions of the Clean Air Act (CAA); discharges of storm and waste waters in accordance with the National Pollutant Discharge Elimination System (NPDES), and the control of hazardous wastes from cradle to grave in accordance with the Resource Conservation Recovery Act (RCRA).

Compliance includes continuous monitoring of air emissions (CEMS) and periodic reporting as required by NPDES and RCRA. Relative Accuracy Test Audits (RATA) are completed annually; plus, the agency conducts unannounced inspections to assure compliance with air and water permit requirements.

DOT’s Pipeline and Hazardous Materials Safety Administration (PHMSA) is responsible for developing and enforcing regulations for the safe, reliable, and environmentally sound operation of the nation’s pipeline infrastructure. It assures compliance with 49CFR193, “LNG Facilities: Federal Safety Standards” and 49CFR192, “Transportation of Natural Gas by Pipeline: Minimum Federal Safety Standards.” The latter pertains to the pipeline that delivers gas from EcoElectrica’s LNG terminal to Prepa’s Costa Sur Power Plant. Annual reporting and inspections are required for compliance.

Occupational Safety & Health Administration (OSHA) assures compliance with 29CFR1910, “Occupational Safety and Health Standards,” and 29CFR1917, “Marine Terminals.” OSHA recommends safety training requirements—including such things as fall protection, confined-space entry, electrical safety, etc.

Puerto Rican agencies

Public Service Commission works in concert with DOT’s PHMSA on pipeline safety (see above). It is certified by DOT to regulate, inspect, and enforce intrastate natural-gas pipeline safety requirements.

Police Dept is responsible for licensing and auditing of facilities handling and transporting explosive substances. Audits are conducted twice annually.

Fire Dept is responsible for the annual inspection and certification of firefighting systems.

Dept of Labor assures compliance with pressure-vessel codes. It inspects and certifies pressure vessels and cranes yearly.

Dept of Health verifies compliance with potable water standards and the facility’s sanitary license. Reporting of monthly sampling and monitoring activities is required.

 

4. Safety paramount in the design of LNG tankers

SB 4 A, B

Personnel at electric generating plants powered by combustion turbines know that natural gas is an inherently safe fuel to transport, store, handle, and burn. For gas to explode, it must be mixed uniformly with air in a concentration of from 5% to 15%, confined in an enclosed space, and ignited.

Preventing uncontrolled releases of gas is the first step in assuring a safe working environment. LNG tankers are conservatively designed to protect against the release of gas in the unlikely event of hull damage. Jeffrey P Beale, president, CH-IV International, describes the three basic types of cargo tank designs in his report, “The Facts About LNG,” available at www.ch-iv.com:

Self-supporting spherical. These ships are easily recognized by the four or five hemispherical domes that protrude above the main deck. The LNG tanks are protected by their location—a significant distance from the vessel’s double hull at the waterline—as well as by a support skirt of high-tensile-strength steel the vicinity of the waterline.Self-supporting prismatic-shaped cargo tanks conform more closely to the shape of the ship’s hull than do spherical ones. Typically, vessels have three or four of these tanks, fabricated independently of the hull and lifted by crane into place; they also have a flat-looking main deck, one resembling that of a conventional crude-oil carrier. Horizontal and vertical stiffeners and bulkheads strengthen the cargo tanks and lock them into position within the hull.Membrane-type LNG carriers are double-hulled—the inner hull supporting the cargo tanks with webs and stiffeners (Fig A)—and usually are characterized by a beveled, raised structure above the main deck as Fig B shows. The general appearance of membrane-type carriers is similar to that of self-supporting prismatic-shaped vessels.Cargo tanks have several levels of protection, as illustrated in Fig C, including the following:

  • A nominal 3/8-in.-thick primary membrane fabricated of stainless steel or Invar. Note that the latter, an alloy containing 36% nickel and 64% iron, has a very low coefficient of thermal expansion. 
  • A nominal 3/8-in.-thick secondary membrane of alloy steel separated from the primary membrane by about a foot of perlite insulation. Perlite is a naturally occurring, lightweight volcanic glass. 
  • Another foot or so of perlite separates the secondary membrane from the nominal 1-in.-thick inner hull.
  • The outer hull (1 to 1½ in. steel plate) forms a ballast tank with the inner hull. The inner and outer hulls are separated by a distance of about 8 to 10 ft.

The S/S Sestao-Knutsen shown in Fig B is typical of the LNG carriers that serve EcoElectrica. It was delivered in late 2007 by Knutsen OAS Shipping of Haugesund, Norway to Stream, a 50/50 joint venture between Repsol and Gas Natural Fenosa for trading, wholesaling, and transporting LNG. Capacity of the vessel, which has an overall length of 933 ft and a beam of 139.4 ft, is 867,990 bbl. Summertime draft is 40.4 ft when the vessel is full. It takes about 16 hours to discharge a complete load of LNG from the vessel.S/S Sestao-Knutsen’s officers hosted the editors during their visit to EcoElectrica. The cross-compound steam turbine plant in Fig D is capable of driving the vessel at speeds up to 19.5 knots. LNG that vaporizes during transport is burned in the ship’s dual-fuel boilers.

SB 4 C, D

 

5. Rollover can quickly release large amounts of boil-off gas

Rollover, a phenomenon conducive to rapid pressurization of an LNG storage tank, is caused by heat leaking into a tank having two layers of LNG with different densities, Arthur Ransome, VP and GM for CH-IV International, told the editors. The following information was developed by Ransome and his colleagues:

To illustrate the concept of rollover, first examine the behavior of a homogeneous mixture of LNG in storage, as shown in Fig A. Here, the convective flow of heat leaking into the LNG creates a natural circulation. The “warm” fluid moves up the tank walls and across the liquid surface, where heat is released as gas boils off. Evaporation of the LNG reduces the surface temperature and the cooler liquid drifts downward, completing the cycle.

SB 5

In a stratified tank (Fig B), the less-dense upper-layer convection proceeds normally, releasing heat in the same manner as the homogeneous case. However, the convective boundary in the dense lower layer is unable to penetrate the upper layer and it forms its own convection pattern. Heat leaking into the lower layer cannot be removed by surface evaporation, so the thermal energy remains trapped. As the temperature of the lower layer increases, its density decreases.

When both layers achieve virtually the same density at the interface, very rapid mixing and the release of the suppressed boil-off occur, causing a rollover (Fig C). An actual flip-flop of the LNG layers does not happen, as the name infers; however, the speed at which heat transfer proceeds can cause substantial turbulence in the tank. Rollovers can be relatively small and insignificant to the vapor handling system—or not. Sometimes, very substantial quantities of boil-off gas can be produced in a short period of time.

Stratification does not occur in a tank of homogeneous LNG. But the introduction of LNG of different density into a partially filled tank can lead to the temporary formation of stratified layers. Another point to remember: Stratification can occur in an idle tank over a long period of time.

The rollover phenomenon can be of sufficient consequence to the operator and owner of an LNG facility to warrant serious consideration on the methods of detection, prevention, and mitigation. There are a variety of techniques and equipment to accomplish these objectives. Perhaps the best way to get started in developing a stratification mitigation plan is to read through NFPA 59A.

Designers take note: The 2001 edition of NFPA 59A (the one referenced in DOT’s 49CFR193 regulations on safety standards for LNG facilities) states in Section 4.1.2.4 that “all LNG containers shall be designed to accommodate both top and bottom filling unless other positive means are provided to prevent stratification.”

Section 11.3.7 provides operations personnel and designers the following guidelines on bulk transfers into stationary storage containers:

  • “The LNG shall be compatible in composition, or temperature and density, with the LNG already in the container.”
  • “Where the composition, or temperature and density, are not compatible, means shall be taken to prevent stratification, which might result in rollover and an excessive rate of vapor evolution. If a mixing nozzle or agitation system is provided, it shall be designed to have sufficient energy to accomplish its purpose.”

 

6. HRSG surface arrangement

Heating surfaces in EcoElectrica’s Alstom heat-recovery steam generators are arranged as follows in the direction of gas flow:

HP superheater
Reheater
Duct burner
HP evaporator
HP economizer
LP superheater
IP superheater
IP evaporator
IP economizer
LP evaporator
LP economizer

 

7. Desalination system provides potable water, boiler makeup for onsite, offsite use

EcoElectrica’s two multi-effect seawater distillation plants, each rated a nominal million gallons per day, are critical to the facility’s operation (Fig A). Product water from the four-effect evaporators, supplied by Israel-based IDE Technologies Ltd, is used to produce steam-cycle makeup for both EcoElectrica and Prepa’s Costa Sur Power Plant as well as potable water for both onsite use and for send-out to the Puerto Rico Aqueduct and Sewer Authority (Prasa).

SB 7 A SB 7 B SB 7 C

Energy for distillation is provided by low-pressure steam (nominally 30 psig) from the heat-recovery steam generator or from the LP turbine bleed (refer to Figs D and E in the main article). The LP steam powers a steam-jet thermocompressor which enables efficient evaporation at low temperatures.

Steam from the thermocompressor enters the first effect’s horizontal tube bundle, transferring heat to seawater cascading down the outside of the tubes (Fig B). The condensate that forms in the tubes flows via a cooler to the condensate storage tank at about 100F. From there it passes through a mixed-bed polisher and is retained in the demin storage tank until needed for cycle makeup. The polisher can process about 4 million gal of condensate before the mixed bed must be regenerated, which is done onsite.

Vapor formed on the shell side of the first effect flows through the tube bundle of the second effect, which operates at a lower pressure than the first effect. The heat transferred to cascading seawater in the second effect creates the vapor used in the third effect’s bundle, and so on. Distilled (product) water created by the condensation of vapor in the second, third, and fourth effects, as well as in the condenser, is cooled to about 95F, and stored in a 400,000-gal tank (Fig C). The distillate product contains less than 5 ppm TDS (total dissolved solids).

Three-quarters of the distilled-water tank’s capacity is dedicated to fire-water reserve. A portion of the remainder is sent to the condensate storage tank, as required, and to Prepa. The balance flows through a remineralization system (Fig D), thereby making the distilled water acceptable for human consumption. Water not required for the plant’s potable and service-water systems is sold to Prasa (Fig E).

SB 7 D SB 7 E

Looking at Fig B, note that incoming seawater (about 88F in summer, 72F in winter) flows through the condenser first. It operates at the lowest pressure in the train of five heat exchangers. Temperature of the brine, and its salinity, increase as the seawater flows from the fourth to first effects. Brine is discharged to the cooling tower at about 140F. Of interest to generation planners investigating sites with ocean access, EcoElectrica’s original seawater piping was stainless steel, but deterioration forced its replacement with FRP.

 

8. EcoElectrica, UPR collaborate on marine environmental science

EcoElectrica’s operations depend significantly on coastal water resources. Since its startup in 2000, the plant has established a comprehensive biological monitoring program to assess the condition of marine ecosystems and the quality of the surrounding water bodies.

In 2011, EcoElectrica began a collaborative research program with the Univ of Puerto Rico’s (UPR) Dept of Marine Sciences (DMS) at the Mayaguez Campus. In that collaboration, I have served as principal investigator on behalf of the university, where I have worked for the past 17 of my 25 years as a marine scientist.

Among other benefits, the collaboration has offered DMS graduate students a unique opportunity to acquire professional experience while applying their knowledge in a “living laboratory.” Thus, EcoElectrica is supportive of the university’s goal of providing hands-on experience to graduate students in marine sciences at various stages of their studies. Since 2011, eleven students have been incorporated into the program, participating in all phases of sampling and analysis.

Graduate students are investigating the dynamics of entrainment and impingement of marine species at the facility’s seawater intake; water currents and sediment composition; water-quality indicators; and the influence of the facility’s process water discharge over corals, fishes, shellfish, seagrass habitats, and other species.

This diversity of topics provides an extraordinary opportunity for students to integrate new knowledge into existing information and develop a better understanding of the complex marine ecosystem dynamics surrounding EcoElectrica. The results of these studies have facilitated the plant’s compliance with its environmental goals and regulatory requirements as well as with the evaluation of ongoing mitigation projects.

In 2011, EcoElectrica donated to the DMS approximately $130,000 in state-of-the-art instrumentation essential to the research and assessment of phytoplankton communities in “La Parguera,” one of the three bioluminescent bays in Puerto Rico. This equipment provided the leverage necessary for obtaining an important fellowship to further the examination of bioluminescent organisms and their relationships with coastal conditions.

The bioluminescent bay at La Parguera is a national treasure and known worldwide. By studying its dynamics, the community at large will have a better understanding of how this delicate ecosystem works and what local residents, tourists, and fishermen, among others, can do to be more responsible when it comes to enjoying its many enchantments.

The collaboration between DMS and EcoElectrica has been extremely successful; the goals established by the plant have been comprehensively met—and even surpassed. At the same time, the university has received the means to support its students with work experiences and access to equipment and materials that otherwise would not have been available to them. This may help students in the development of new ideas that may result into tangible products for the present and future.

SB 8I feel great satisfaction in having the opportunity to spearhead the efforts on the academic side. The experience has been of incredible personal and professional growth, not only for the students but also for myself. EcoElectrica’s management has been unconditionally supportive to the program and has attended to all the necessities that have emerged in its implementation. My commitment is to keep strengthening the relationship every year, and with the support of the students and our EcoElectrica partners, take it to the next level.

Dr Ernesto Otero Morales
Principal Investigator
Dept of Marine Sciences
Univ of Puerto Rico, Mayaguez Campus