The multi-year, multi-faceted Emissions Reduction for Legacy Engines (ERLE) program to develop cost-effective NOx controls for pipeline reciprocating compressor engines has entered into its final stage with the field testing of three engines that are in mainline compression service. ANR Pipeline (TransCanada) has installed retrofit equipment on two 12,000 HP Clark TCVC-20M engines at their Eunice, LA station, and Southern Natural Gas (El Paso) has installed retrofit equipment on a 4000 HP Clark TCVA-10 at their Gallion, AL station. These two sites will serve to evaluate the success of the ERLE program in achieving its primary objectives of:
The ERLE program has targeted the creation of a toolkit of technology options that operators can use to achieve the variety of NOx reductions they will require in different circumstances, on different engines. This is premised on the fact that retrofit technologies can combine in different ways to achieve different NOx control levels – with different layers of technology providing incremental NOx reductions and more sophisticated engine controls, increased reliability, and reduced maintenance
These field test engines are configured such that they have the ability to evaluate the incremental NOx reduction and performance impact of the different technology layers that comprise the ERLE toolkit.
ANR-Eunice: These two engines, at 12,000 hp each, are some of the largest individual integral compressor engines in the US. This field test will focus on NOx control across the full operating range of the units, and assess the effect of turbocharger upgrades and monitoring. For most NOx retrofit projects, the turbocharger and associated air delivery system represents by far the largest cost element. The two Clark TCVC-20M’s, while otherwise nearly identical, have very different air handling capabilities. One has two new, larger turbos and turbo performance monitoring systems (TurboShield, a PRCI R&D product marketed by Exterran) while the other kept its legacy turbo configuration (with no performance monitoring). The combustion and control systems are identical – each have an electronically-controlled high-pressure fuel injection system, pressure-based cylinder balancing, electronic-controlled precombustion chamber fueling, and ion-sense-based prechamber balancing. The Eunice station has a challenging annual NOx and CO tonnage limitation, and these engines face an operating environment that requires a wider operating range than historically experienced – notably at low loads. In fact, the improved control provided by the ERLE technologies is expected to allow the units to recover lost HP by operating at a higher torque at lower speed, as TCVC-20M’s have historically been difficult to operate at their rated speed. Performance testing will continue through the summer, with full emissions tests accompanying these evaluations.
Southern Natural – Gallion: This 4000 HP engine was operating in a mode that is a classic challenge for pipelines , it met its NOx and CO permit levels – both below 3 grams - yet required careful monitoring to ensure the margin of compliance was adequate. This unit experienced a trade-off of increased CO for incremental NOx reductions that is not uncommon for many engines, and which limits the NOx reduction compliance margin attainable with the as-found system. The field test is expected to relax that constraint. The field test equipment configuration is electronic controlled high pressure fuel injection, pressure-based balancing, electronically-controlled prechamber fueling, and ion sense-based prechamber balancing. Gallion has the ability to evaluate the impact of the ERLE technology layers by disabling the auto-balancing feature, and by disabling one or both of the enhanced control features on the precombustion chambers that are the key component of this ignition system (this unit uses two PCC’s per cylinder). Thus, a stepwise evaluation of the incremental values of the technology layers is possible, and with all layers activated, this unit is expected to be able to achieve very low NOx emissions with no CO limitation or fuel penalty due to combustion instability. Baseline testing is complete, and performance/emissions tests will continue into the fall.