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HRSG cleaning is an effective way to restore lost performance because it reduces the back-pressure on the gas turbine, thereby increasing the net power output and reducing cost of fuel per MW generation.
Every additional half-inch (water column) of pressure drop through a typical F-class HRSG reduces the bottom line by about $100,000 per annum, depending on the price of fuel. An effective cleaning could be expected to regain at least 3-6 inches of pressure drop.
Check out the case study below to learn how a combined cycle plant recently saw a 41-day payback from their HRSG cleaning.
Why is this so important?
Fouled heat recovery steam generator (HRSG) tubes penalize plant performance in several ways. Fouling of the gas-side HRSG tubes increases a plant’s heat rate by reducing the heat transfer and increasing the back-pressure of the gas turbine. Reduced heat transfer efficiency also reduces the output of the steam turbine, and excessively fouled HRSGs can exceed their designated back-pressure limit, triggering an expensive and automatic “turbine trip” or curtail otherwise available generation.
How to choose a cleaning method:
It is important to evaluate what methods have typically been available and what limitations and risks come with them. Common off-line cleaning methods such as dry ice blasting require scaffolding or Sky Climbers that are expensive, time-consuming, and maybe only marginally effective due to limited penetration or cleaning influence in the densely packed finned tube bundles. Another is a pressure-wave cleaning method that utilizes repeated insertion of bags containing combustible gas that are dangled at various elevations and detonated in open voids near the heat transfer surface, but may be expensive, time-consuming, and repeatedly cause superfluous impact to surfaces, equipment and structural components that are virtually non-essential to improving efficiency or enhancing the objective for cleaning.
A new solution based on 14 years of proven technology is safely providing highly beneficial results to combined-cycle plants. The off-line application of this substantiated pulse-detonation cleaning technology, utilized routinely on-line for 24/7/365 performance, has recently demonstrated dramatic improvements in off-line cleaning results of severely fouled, tightly packed finned harps in HRSGs when compared to existing methods. As an example, one recent application to a Nooter/Eriksen unit resulted in a 4” CT decrease with a net payback of just 41 days based on full load performance.
What makes EPIC Off-line HRSG Cleaning Unique
Off-line pulse-detonation, or “shockwave,” cleaning technology provides several advantages over other cleaning methods:
- Effective, safe and targeted cleaning energy: Over the past 14 years, shockwave cleaning has proven to provide penetrating, all-encompassing cleaning energy that can extend far into the tube bank and effectively dislodge deep and impacted deposits from heat transfer surfaces.
- Frequently reduced cleaning time, shorter outages: The technology employs an automated cleaning rig that can navigate quickly across the heat transfer surface without the need for scaffolding or man-baskets, significantly reducing overall cleaning time compared to other methods.
- Extremely safe for personnel and the surrounding structure: The shockwave cleaning energy is remotely generated safely within the specially engineered combustion tube and then exhausted directly and focused only at the heat transfer surface so the surrounding structure is not exposed to indiscriminate and potentially harmful explosions, while all personnel are located securely outside the structure throughout the cleaning process.
Case study: Effective HRSG Cleaning with Off-line EPIC Shockwave Technology at a Florida Combined Cycle Plant
Problem:
A Large combined cycle plant needed to remove surface and embedded oxidation and operational deposits from a Nooter/Eriksen HRSG unit. They were experiencing restricted CT backpressure and insulated crucial heat transfer surfaces, which was affecting their overall efficiency and performance.
Solution:
Using the proprietary EPIC ™ cleaning system expertly executed by Thompson, this method utilizes shockwave displacement energy generated from the patented IMPULSE® cleaner to safely and effectively concentrate a repeated series of dynamic high-pressure cleaning pulses directly and deeply into the tube bank. The cleaning is coordinated via a remotely-controlled navigation system with all personnel located safely outside of the HRSG unit.
The automated and remotely operated EPIC cleaning system is extremely safe for personnel as well as the entire HRSG structure with numerous fail-safe features fully integrated into the overall process. Implementation of this EPIC off-line application, based on 14-years of proven on-line pulse-detonation shockwave boiler and HRSG cleaning experience, delivers dramatic 360-degree results-focused solely on the fouled heat transfer surfaces within a HRSG.
Results:
The EPIC™ cleaning system effectively dislodged and removed the deep and heavily impacted deposits that had accumulated on and within the finned tube surfaces of the HRSG. The post-cleaning visual inspection throughout the HRSG, complimented by penetrating in-depth videoing into multiple harp panels by borescope, combined to provide clear evidence of the EPIC cleaning effectiveness. The operating performance was later evaluated by plant engineering and management personnel resulting in comments such as one from the Operations Manager being “thrilled” with the results and the Plant Manager enthusiastically stating “EPIC is the way to go to clean our HRSGs and we’ll use it again in the spring for our next one.”
Based on 6-month comparative operating data that was voluntarily shared with Thompson, it was determined that the combustion turbine backpressure was reduced by 4 inches of water column, resulting in a heat rate decrease by roughly 0.5 MMBtu/MWh. This was computed to yield an equivalent payback in 1,018 hours (41 days) due to reduced fuel costs, based on a 100% production (MW) load.
The negative effects are undeniable: Fouling on the gas side of HRSG tubes compromises plant performance. But you can restore lost performance through innovative HRSG cleaning that reduces back-pressure on the gas turbine, increasing net power output. Through this method, combined-cycle facilities are regaining 3-6 inches of pressure drop and increasing their bottom line by $600,000 a year or more annually. This highly safe and effective cleaning technology provides penetrating, all-encompassing cleaning energy that dislodges deeply impacted deposits from heat transfer surfaces far into the tube bank. When it comes to safety considerations of various HRSG cleaning techniques, automated methods like off-line pulse-detonation cleaning technology reduce hazard exposure, cleaning time and outage duration.
For more information contact Carl Wise at 910-612-5468, 800-849-8040 or cwise@thompsonind.com
Or visit thompsonindustrialservices.com/EPIC