Availability Study Improves Revenue and Optimizes Equipment Configuration
Reliability, Availability & Maintainability (RAM) Study
50 Words or Less
By employing our RAM study methodology, our client sells more product because they can produce more steam. In this case, greater steam generating flexibility with fewer maintenance requirements clearly provided higher steam availability over time, yielding an annualized revenue improvement of up to $6.1 million.
Once-through steam generators, also known simply as boilers. These produce 77% quality steam.
Our client, a Canadian oil-sands (bitumen) producer, has a facility in Alberta to recover and upgrade bitumen reserves. Their primary method of recovering bitumen is through a Steam-Assisted Gravity Drainage (SAGD) process whereby steam is injected into the ground to reduce the viscosity of (soften) the bitumen so that it may drain into a lower wellbore and be pumped to the surface. This client already has one operational SAGD field and is performing the front-end engineering and design for a second SAGD field.
Consistent and continuous steam production is very important to SAGD operations because of the “steam chamber” that forms underground. To produce a steady supply of bitumen at the surface, this steam chamber must be stable and growing to come in contact with the bitumen reserves. To maintain a stable and growing steam chamber, one must supply a consistent and continuous volume of steam. If steam production is lost or reduced, the steam chamber will start to collapse and may require several days of steam injection to re-stabilize the steam chamber and begin producing bitumen again.
Therefore, to make better steam production capital investment decisions, the client asked us to perform a RAM study of two steam generation equipment configurations to determine the configuration that yields the highest steam On-Stream Factor (OSF). Knowing how equipment configuration affects steam production (and ultimately bitumen sales) helps our clients make better informed decisions and aids in establishing (or refuting) the economic justification of capital expenditure.
Steam Generation Equipment
We were asked to evaluate two basic options: A) use two combustion gas turbines (CGTs) with heat recovery steam generators (HRSGs) and one once-through steam generator (OTSG, i.e. boiler) to generate steam, or B) one CGT with five OTSGs to generate the same quantity of steam. See Figure 1 below for a comparison of the configurations. Option A has fewer points of failure; option B is more flexible. For both options, it is imperative to have a very reliable steam production configuration to protect the stability of the underground steam chamber.
Though there is more equipment necessary to produce steam beyond those shown, these are the most prominent items in the system and thus the only ones modeled.
Water Supply & Treating
No matter how you generate steam, you need high-quality water to run boilers reliably for extended periods. For this reason, both configuration options utilize two Hot Lime Softeners to reduce the mineral content in the boiler feed water. When a softener is offline, only half the boiler feed water is available to produce steam, and thus only half the steam can be produced. And again, while there is more equipment necessary to supply and treat water, the Hot Lime Softeners are the only ones included in this study.
With all reliability studies, good failure data is fundamental to providing meaningful results. As the adage goes, garbage in: garbage out. For all BBA studies, we use a combination of trusted failure data sources from industry and vendor databases. All data undergoes a thorough vetting process with the project team before it is used in any study.
Figure 1 – Availability Block Diagrams (ABDs) of the two equipment configurations evaluated.
All of the equipment items in this study undergo periodic scheduled maintenance activities. For this study, modeling the Hot Lime Softeners is important because they experience a scheduled annual outage with a one-week duration. It makes operational sense, then, to “shadow” scheduled boiler maintenance activities within these softener outages, thus minimizing the overall downtime.
With option A in particular, it is important that the annual combustion turbine maintenance activities be shadowed within the softener outages. If for some reason turbine maintenance cannot coincide with softener maintenance, a significant reduction in steam on-stream factor will result.
With Option B, however, if the single turbine’s maintenance cannot coincide with one softener’s maintenance, it would simply be scheduled to coincide with the other softener’s maintenance activities. Additionally, OTSG boiler maintenance can be scheduled anytime outside of turbine maintenance as any single OTSG can be offline without affecting steam production.
Performing sensitivity cases is the best use of any RAM study. Sensitivity cases allow you to evaluate the “what if” scenarios to optimize the system configuration. In this study, the following sensitivity cases were evaluated:
What if Hot Lime Softener maintenance need only be performed every 2 years instead of annually?
What if once every three years the scheduled maintenance for turbine #1 cannot be shadowed by the scheduled maintenance of Hot Lime Softener #1.
General Results & Conclusions
After carefully modeling and studying this system, Option B, with greater flexibility with less maintenance requirements, clearly provides the most available steam over time. As can be seen in Table 1 below, the long-term On-Stream Factor (OSF) for Option B is consistently 0.3% to 0.4% higher than for Option A. On an annualized basis, 0.3% translates to increased revenue of as much as $6.1 Million per year.
Table 1 - Overall Results
Even without any scenarios, Option B produces more steam than Option A.
For case 1, Option A sees no benefit because though the Hot Lime Softener maintenance interval is doubled, the turbine maintenance interval is not. Option B improves in case 1, however, because maintenance of any single boiler does not impact steam production. Therefore, reducing Hot Lime Softener maintenance improves overall steam production for Option B.
For case 2, both options see a reduced steam production of 0.2% from the base-line, but Option B is still produces more steam in the long run than does Option A.
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