emissions reduction and horsepower re-rate

Emissions Reduction and Horsepower Re-rate: A Case Study 2006 Gas Machinery Conference Oklahoma City, OK Page 1 of 9

Emissions Reduction and

Horsepower Re-rate:

A Case Study

Presented at the 2006 Gas Machinery Conference

By:

Jerry Creel El Paso Corporation Dustin Malicke Hoerbiger Engineering Services

Fred Basin Hoerbiger Engineering Services


Requirements In 2003 the El Paso Corporation, Southern Natural Gas facility located near White Castle Louisiana, was required to propose a plan for reducing the station NOx emissions by 80%. There were 10 units located at the facility, 3 of which were low horsepower (550 hp each) engines. The remaining 7 engines were comprised of 3 GMVA-8s, 1 GMVA-10, 2 GMVC-10s and 1 GMVH-12. El Paso commissioned a study to determine the best approach to achieve the State of Louisianas emissions mandate. The results of this study produced a project scope requiring retirement of the 3 smaller engines and re-rating of the 7 remaining engines to maintain the FERC permitted station horsepower. This had to be accomplished while achieving the required NOx reduction. El Paso let the project for bid in the fourth quarter of 2003, and Hoerbiger Engineering Services (then Gas Engine Systems) was awarded the contract for the on-engine work while other contractors were awarded the off-engine design and construction. The concepts employed to arrive at this solution was presented in the 2005 GMC paper Considering the Options, presented by Tom Burgett and Hans Mathews. This paper brings the details of a real project and the operation results to those who may be faced with similar opportunities. Implementation The modification of primary interest to this discussion is the horsepower re-rate and how it was achieved. Six of the seven units were equipped with the original centrifugal blowers, which draw a substantial amount of parasitic horsepower from the units. Removing those blowers allows said horsepower to be redirected to a more useful purpose; i.e. moving gas down the pipeline. The net effect is little change to the indicated load on the power side of the engine, just the distribution. The re-rate called to take the ratings of the GMVA-8s from 1100 to 1400 hp, the GMVA-10 from 1350 to 1700 hp and the GMVC-10s from 1800 to 2000 hp. With the end state now defined, each engine/compressor and its supporting systems were evaluated to determine where modifications or additions were required. In evaluating the units, it became clear that four unique solutions would have to be developed because each group had its own unique characteristics. The solutions could be broken down into four groups, GMVA-8, GMVA-10, GMVC-10 and GMVH-12. All engines already had a high energy ignition system installed and they all would receive a high pressure fuel injection system along with an automatic balancing system. The requirements for each of the four groups is listed in Table 1 and described in detail below.

Table 1: Solution Matrix

GMVA-8 GMVA-10 GMVC-10 GMVH-12 Turbocharger New New New Modify Intercooler New New New New Exhaust Manifold New Adequate Adequate Adequate JW Cooling System Adequate New Adequate Adequate Aux Cooling System New New Modify Modify Lube Oil System Adequate Adequate Adequate Adequate Muffler New New Adequate Adequate Filter/Silencer New New Adequate Adequate Automation Modify Modify Modify Adequate Compressor Cyl Modify Modify Adequate Adequate


As part of the project, all centrifugal blowers were removed from the GMVA and GMVC series machines and new ABB turbochargers were installed. The air specifications provided by HES for the GMVA and GMVC engines were such that ABB was able to use just two different design turbochargers for all six engines. The eight cylinder engines were of one turbocharger design while the ten cylinder engines were of another even though there is a 300 horsepower difference between the two types of ten cylinder engines. This reduced the costs associated with the design, installation and maintenance of the turbochargers. The GMVH received turbocharger modifications to the existing ET18 turbocharger to enhance the air delivery. The increased air delivery required installation of new intercoolers on all units to achieve the required air manifold temperatures. To simplify the installation and reduce costs a single intercooler was used on all units except for the GMVH-12. This unit retained its existing turbocharger which had a dual outlet compressor. Two new intercoolers were designed to fit in the stock location with minimal modifications to the existing piping required.

The exhaust manifolds on the GMVA-8 engines were water cooled; all other units were originally installed with dry (non-cooled) exhaust manifolds. When turbocharging an engine, it is important to deliver as much of the exhaust energy to the turbocharger as possible. Converting the GMVA engines to a dry exhaust manifold has two benefits; it delivers as much energy as possible to the turbocharger and it reduces the heat rejection requirements for the engine. This freed up heat capacity of the jacket water cooling system can be used elsewhere. In the case of the GMVA-8 engines, it was used to cool the water jackets of the turbocharger. This allowed the jacket water cooling system to be used without modification. The lack of a wet exhaust manifold on the GMVA-10 and the poor performance of the existing cooler resulted in a completely new air cooled heat exchanger being installed for this unit. The jacket water system for the GMVC-10 engines was adequate because the new turbochargers installed had a lower heat rejection requirement than that of the turbochargers that were removed. For the GMVH-12, no modification were made that affected the jacket water system, therefore its system was adequate. The GMVA engines did not have an auxiliary water cooling system. Instead, all units cooled the oil by pumping it out to a panel in the air cooled heat exchanger. For the GMVA-8 engines, the oil panel was converted to an auxiliary water panel and a supplementary cooler was installed to provide the required auxiliary water cooling. The auxiliary water was used for the intercoolers and for the newly installed shell and tube heat exchanger for the lube oil. An electric driven


pump was installed in lieu of replacing the engine driven jacket water pump with a dual pump setup. The electric pump option was cheaper to purchase and install due to the amount of piping modifications required to convert from the single to the dual engine driven pump. The same approach was used for the GMVA-10 engine except the new air cooled heat exchanger installed for it contained one panel with enough capacity for the auxiliary water requirements.

The GMVC-10 engines and the GMVH-12 engine were delivered with auxiliary water cooling systems. Each of these systems was not adequate for the new operating conditions and was modified by installing a supplemental cooler in series with the existing cooler and upgrading the engine driven pump. The lube oil system for all engines was deemed adequate for the post conversion operating conditions. The ABB turbochargers installed have a self contained oil system and do not require oil supply or cooling from the engine. The lube oil requirements for the ET18 turbocharger on the GMVH-12 engine did not change as a result of the upgrade. The intake and exhaust systems were evaluated initially on their suitability to handle the new flow rates and filtration requirements for the turbochargers. All of the filters and silencers were deemed adequate in the initial evaluation. The data in Table 2 shows that the air flow through the units with gear driven blowers actually decreased after installing the turbochargers. This is due to the turbocharger introducing a restriction in the exhaust system that much greater than any other


restriction in the system. It is this restriction (the turbine side of the turbocharger) that has the largest effect on determining the air flow through the engine.

Table 2: Unit Airflow

Unit Type

Pre Retrofit Air flow (scfm)

Post Retrofit Air flow (scfm)

% Change

GMVA-8 5,500 4,574 -17% GMVA-10 6,143 5,137 -16% GMVC-10 7,726 7,759 0% GMVH-12 8,446 10,100 20%

The filters and mufflers where then evaluated based on the noise criteria of the location. The addition of a turbocharger adds additional noise sources to the engine. The GMVA units did not have inlet silencer installed, only filters, but the GMVC and GMVH units had inlet filters and silencers installed. After the evaluation, it was determined that the GMVA units would need new inlet silencers and new mufflers in order to meet the required noise criteria. The equipment for the GMVC and GMVH units was deemed adequate for the post retrofit service. El Paso elected to replace the air filters on the GMVA units with a combination filter silencer for this application instead of adding a separate inlet silencer in the inlet piping. The White Castle station was automated before the start of this project but each group of units was automated to different degrees. The GMVH-12 was the only unit that was fully automated and included an air/fuel ratio controller. As part of this project, new unit panels were installed on all of the units similar to the existing panel on the GMVH-12. The panels were design to accommodate the new high pressure fuel injection system and the automatic balance system. Before the start of construction for the engine retrofits, El Paso contracted to have the new panels built, installed and commissioned.


In order to utilize the additional brake horsepower, the compressor cylinders needed to be properly sized for the new operating conditions. The compressors for the GMVC units were determined to be capable of achieving the new rated horsepower with their current configuration and the current pipeline operating conditions. The compressors on the GMVA units were known to be undersized for the units in their current configuration with the current pipeline conditions. The evaluation of the compressor cylinders on these units determined that they could be bored to achieve the desired results. They GMVA-8 units would also receive additional unloaders to enhance their operational flexibility. The final piece of the puzzle was to evaluate the station air, electrical and fuel gas systems. The addition of six turbochargers with jet assist greatly increased the demand of the starting air system. The evaluation of the system revealed that the station needed to add both storage and compression to the system. The addition of the controls and electric motors increased the electrical demands but the evaluation showed that the station still had excess backup generator capacity after the new systems were installed but the purchased power needed upgrading. To prevent the units from shutting down during a power outage a UPS system was installed that supplied power to the control system, fuel injection system and ignition system. This allowed uninterrupted operation until the backup generator came online in the event of a power outage. The installation of the high pressure fuel injection systems required that a new fuel gas system be installed to support it. The current system was unable to be up-rated to the new operating pressure without significant and costly modifications. In addition, the current system would have to remain to operate the facility until all units had been retrofitted.


Results This project achieved the desired goal of meeting the regulatory mandate for emissions reductions. In doing so several benefits where also realized. Each engine realized a three to 8% reduction in heat rate after the retrofit as shown in Table 3. The average heat rate for the station (weighted by horsepower) was reduced by 12 percent. This is partly due to the retirement of the three small engines that were not very efficient (heat rate of approximately 11,000 btu/bhp-hr). The remainder was due to the technologies employed and the removal of the parasitic load of the gear driven blowers from six of the units. The use of the high pressure fuel injection system resulted in lower requirements for air from the turbochargers. This affects both the build of the turbocharger and the requirements for the cooling system to reject the additional heat created to produce the additional combustion air.

Table 3: Engine Heat Rates

Unit Type

Pre Retrofit Heat Rate

(btu/bhp-hr)

Post Retrofit Heat Rate

(btu/bhp-hr) %

ChangeGMVA-8 7700 7150 -7% GMVA-10 7700 7100 -8% GMVC-10 7400 7000 -5% GMVH-12 6700 6475 -3%

Lessons Learned As those in the project business know, no project ever is without its issues. There were several lessons learned while performing this project that bear mentioning here to prevent the same from happening to others in the future. The first and foremost item is planning and scheduling. It has been said that you can never plan enough. You need to develop a good, and realistic, plan in the beginning and keep adjusting it as required throughout the life of the project. In this industry scheduling outages for engine retrofits can be quite challenging. You need a schedule that works for all parties involved but one that is still realistic. While an aggressive schedule may look good on paper, and seem achievable while everyone is sitting around the table, it is rarely achievable when put into action because of all the external influences beyond the project managers control and the finite amount of resources available within this industry. The top lesson learned directly related to the engine up-rate process is that of engine health. The engine must be in great condition before you start the retrofit process or you will suffer the consequences later on. It is worth the extra time and effort to thoroughly evaluate the health of the unit and all of its components. Of particular interest is the health and design of the power cylinders, heads, pistons, rings and piston carriers. While all of the engine components should be verified to determine if they are suitable for the new operations these are of the most common items to find differences in or issues with. For most pipeline engines in operation today there is a wide variety of different configurations of heads, power cylinders and pistons. While you may not have to upgrade to the latest OEM design for a particular component, you need to insure that the engine contains the same version of each component and that all the components are compatible with each other. It is also very important to verify the calibration of all end devices related to air / fuel ratio control prior to startup.


The health of the cylinder liner and the ports is extremely important when up-rating the unit or just adding a turbocharger to a unit. If a cylinder has ports that are plugged with carbon then the ability of that cylinder to properly breathe and scavenge will be significantly reduced.

Modification of the compressor cylinders can be accomplished in several ways, depending on the required bore increase. In this instance the cylinders were capable of supporting the increase. The chosen method, which appeared to be the most cost effective at the outset, involved removing the cylinders and performing the modifications offsite. Other options were to replace the liners with new units of the correct bore size or overbore in place. While all of the options have certain advantages and disadvantages, it should be mentioned that removing the cylinders opens the door to alignment issues during re-installation. The specifications and methods for assembly have changed since the original construction of these stations. This resulted in having to remove and modify suction and discharge bottles. Another issue that affected the scheduling of the project, and couldnt be predicted beforehand, was encountering porosity in the liners when they were machined to the new bore size. The up-rate and emissions reduction can make the engine more sensitive to abnormal operating conditions or upsets in the operating condition. This requires that the control system be able to tightly control the operating parameters of the unit. The unit in OEM configuration was able to reliably operate over a very wide range of air/fuel ratios. The rich limit was defined by when the unit would start to go into detonation. The lean limit was defined by when the unit would start to misfire. If the controls operated the unit anywhere in between then the unit would operate satisfactorily. The unit must operate within a much narrower window after the unit is up-rated and, more importantly, the emissions limit is imposed. The lean limit is still defined by when the unit starts to misfire. The rich limit is now defined by the maximum allowable emissions. This forces the owner to operate the unit much tighter and closer to the lean limit than before. If the unit is allowed to operate too lean then the possibility of a lean misfire detonation cycle becomes more likely.


Conclusions This project showed that an effective way to meet the emissions mandate is not necessarily the traditional way. By thinking outside the box a new solution was found that was good for both the environment and the company. By retiring the three small units and distributing the power among the remaining units, a solution was found that met the regulatory requirements, increased efficiency and reduced the number of power and compression cylinders to be maintained. The final analysis to be conducted is a financial one. One might ask was this the most economical solution to achieve the desired results. The on-engine portion of the work was performed for approximately $300 per horsepower. If one takes that the off-engine portion of the work was similar in costs then you arrive at about $600 per horsepower for the complete project. This is less than half of the cost when compared to the industry rule of thumb of approximately $1400 per horsepower to install new compression. One may challenge that by not retiring the three small engines, you could have saved money. If you did not retire those units, then you would have to apply emissions reduction technology to those units. You would not have saved any more by not up-rating the GMV engines at the facility because all of the technology employed in the engine up-rate and emissions reduction would be required if you retained the original power rating and only reduced the emissions to the required levels. The benefits of this approach to the emissions reduction mandate resulted in a solution that allowed the operator to meet the required emissions reductions at the facility while maintaining its operational flexibility and enjoying a overall more efficient engines. The outcome of this project showed that it is possible to take a regulatory mandate and use it as an advantage for the company. The result of applying technology is to reduce the emissions at the facility while taking a new approach and increasing the efficiency of the fleet of engines at the same time.

emissions reduction and horsepower re-rate

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