Natural gas resources of all kinds continue to be exploited at an accelerating pace. There is growing worldwide interest in increased development of both conventional and unconventional sources of gas, including shale gas. Consequently, engineers are in the spotlight to design flexible midstream infrastructure to process gas and associated liquids efficiently, rapidly and for maximum profitability. Adding to the pressure on process engineers, project parameter and goals are more than ever a moving target.

Several innovations in software used by process engineers have begun to show results in the past few years, assisting in this dynamic environment. This article looks at two case studies that each demonstrate the use of advanced tools and work flows. The net result of each is a significant business benefit to the facility owner-operators and, in the second case, to the engineering organization. These are reflected in reduced capital requirements and better overall project payback and lifecycle profitability.

BACKGROUND

Process simulation modeling systems have become an essential part of design or revamp and optimization of gathering systems, pipeline transportation, gas separation plants, sweetening units, dehydration units, NGL plants, and the like. These tools have largely replaced the use of spreadsheets or other calculations, even at the feasibility stage of a project. Key reasons for the use of models is their flexibility when the project developer changes design objectives midway in a project, along with the ability to more accurately predict operating performance. However the models, used alone, have some limitations. Most importantly, a project investor or capital investment executive needs to know the capital and operating costs of a proposed project as part of their decision-making process. Also, engineers need good ways to easily compare design alternatives and communicate the analysis and alternatives to others.

One of the innovations introduced by Aspen Technology is the embedding of rigorous capital estimating models so that they can be activated by the process engineer from within the process simulation model. Another innovation is the close integration of the simulation model with a so-called simulation workbook, in Excel, that can be used to both perform sensitivity analysis on the process model flow sheet and also to display key parameters of each alternative for management review. [Reference 1]

CASE STUDY 1: Troubleshooting a gas booster station and dehydration unit.

One of the organizations that has recently used the integrated modeling-economics approach is Kuwait Oil Co. (KOC). KOC was faced with a gas dehydration package that was underperforming and targeted for revamp or replacement. Management was initially leaning strongly toward the revamp approach, as being intuitively the better economic alternative. However the engineering team, led by senior process engineer, Venkata Madhusudana Rao Kapavarapu, was given the opportunity to conduct a comparative analysis of several options, using process simulation models integrated with estimating models, and reliability and maintenance prediction tools. [References 2, 3]

The revamp approach involved achieving reduced water content of the export gas and reducing combined glycol loss, through replacement of column internals, new elements in the absorber unit, and other fixes. Modeling of this approach showed, as expected, lower capital costs for this approach. However the overall negative operating profitability impact was significantly higher due to several factors, including higher predicted maintenance and component replacement incidence, aging equipment, as well as a revenue hit from the process train shutdown period for the revamp project.

The replacement approach involved installation of a totally new gas dehydration unit in parallel and then switching over production. Modeling of this approach, combined with the economics modeling, show a higher capital cost, but a significantly lower overall lifecycle cost due to reduced maintenance incidence, slightly better predicted gas yields, and significantly higher revenue because of a much shorter shutdown period, along with the ability to run the old unit up to the time to switch over to the replacement dehydration unit.

The integrated workflow, in which the process model for each alternative was able to feed into the economic model and rapidly project relative operating and capital costs with +/- 35% reliability, proved to be a critical tool in convincing management to go forward with the replacement unit. Without these tools, engineers may never have had the opportunity to seriously consider the replacement option. Most would probably not have been able to present credible cost information for decision-making due to the time and effort, which would have required a completely separate department’s involvement: the estimating group. This would have forced KOC into the more conservative approach.

The net result of selecting the replacement unit option was a projected annual savings of 20% in operating costs, 30% in spare parts costs, and 20% in insurance premium costs for the dehydration unit. Also project life cycle was optimized and the production facility availability was increased.

CASE STUDY 2: Increase Capacity of a Gulf Coast NGL Facility by 30%

Burns and McDonnell, a mid-sized engineering and construction organization, employed a similar strategy in a recent revamp project performed for a U.S. Gulf Coast midstream client. Working within multi-dimensional project constraints, Elliott Robertson, process engineer at Burns and McDonnell, reported that the use of modeling, economics and simulation workbook provided a powerful integrated toolset to evaluate a number of design alternatives and estimate costs to within 30%. [Reference 4]

Some of the challenges in performing this project were feedstock and product logistics uncertainties, multiple plants and business units, stringent real estate constraints, a fast track schedule, and a project team with mixed experience, not to mention several different existing simulation models describing units within the target facility undergoing revamp.

To address these challenges, Burns and McDonnell adopted some innovative approaches, integrating several engineering tools into a workflow that reduced the project cycle time, improved project team communications, and most importantly enabled better analysis and comparison of alternatives leading to better overall design results and capital costs.

The use of the simulation workbook enabled Robertson to present multiple design alternatives to the entire team as work proceeded, and then to serve as a communication method to the multiple business units of the client-side team. Three separate process units within the NGL facility were modeled, and for each unit the cases analyzed included a base case, economic base case and future design case. The workbook view enabled the team to study feed conditions, product uplift, and key unit constraints. The unified approach also enabled a better and more holistic analysis of suitability of existing equipment and optimization of capital spend, based on the governing rating cases.

The benefits seen by both Burns and McDonnell and their client included minimizing new equipment, improved constructability, reduced project duration and maximized product yield.

SUMMARY

Both of these organizations, Kuwait Oil and Burns and McDonnell saw the opportunity to use newly available software innovations, and were able to adopt these tools, self-train themselves using online training resources, use them on real projects, and most importantly achieve business impact, with very little lead time. Introducing economic models, such as AspenTech’s capital cost estimating models, into the simulation models empowers process engineers to meet management objectives of accelerating project timetables and understand the impact of their engineering decisions on project costs much earlier in the design process.

As the pace of development of gas processing and delivery infrastructure continues unabated, the ability to adopt and effectively use these tools quickly is a key advantage for process engineering teams. Understanding the costs of a proposed design is no longer a luxury but a business imperative today.

REFERENCES:

(1) Beck, R P, AspenTech. “Improve Decisionmaking for LNG project via an integrated technology”, Hydrocarbon Processing. July, 2011, pp 51-54.

(2) Kapavarapu, Venkata Madhusudana Rao, Senior Process Engineer, KOC. “Project Optimization at a Conceptual Level by using Aspen HYSYS and Aspen Integrated Economics”. May 23, 2011, AspenTech OPTIMIZE 2011 Global Conference, Washington DC.

(3) Kapavarapu, Venkata Madhusudana Rao, Senior Process Engineer, KOC. “Process Optimization using Simulation and Integrated Economics”. Oct 24, 2011, MEPEC Conference, Manama, Bahrain.

(4) Robertson, Elliott, Burns and McDonnell, “Use of Aspen Plus, Aspen Capital Cost Estimator and Aspen Simulation Workbook in the Front End Loading Process for a Fast-Track NGL Expansion”. May 23, 2011, AspenTech OPTIMIZE 2011 Global Conference , Washington DC.