Achieving more from a single modelling environment

Paul Boughton

How process software transforms acid gas cleaning and delivers industry first in pressure safety valve sizing. Ron Beck reports.

The oil, gas and petrochemicals industries face global pressure to improve the design, management and operation of their plants to improve profitability. Engineers are responding by evaluating more aspects of process design at the conceptual front end such as safety, capital costs, operating costs, energy usage, quality and capacity.

Process modelling software provides substantial economic benefits throughout the process engineering and asset lifecycle. It brings the power of process simulation and optimisation to the engineering desktop and delivers a unique combination of modelling technology and ease of use. The latest process optimisation software enables companies to efficiently bring new plants to market faster, de-bottleneck processes and optimise production for a higher return on investment.

Typically, modelling acid gas removal ('Gas Treating') and overpressure protection systems existed as stand-alone modelling activity in spreadsheets or isolated models. This perpetual, iterative and manual process leads to sub-optimal results and inefficient workflow. Executing projects faster while meeting changing parameters is a key challenge. Equally, adhering to strict constraints for environmental and safety rules is vital for project success, as is minimising performance degradation and plant disruptions.

For engineering companies, the business opportunity is to provide clients value-add engineering, which entails achieving projects that attain minimum capital and operating costs and improved maintainability. Therefore, the ability to see the process, energy and economics trade-offs, make decisions that improve sales gas quality and minimise carbon footprint will provide a competitive advantage. Another key challenge is to reduce the learning curve for process engineering models. A new generation of the process engineer’s workspace employs user interface paradigms from Office 2010 and mobile devices to improve the user workflow, usability and accessibility of powerful tools.

For upstream, midstream and refining operators and the engineering companies that serve them, Aspen HYSYS is used for all phases of process design and operations. Acid Gas treating and Pressure Safety Valve Sizing are two critical activities that process engineers can now perform directly in the Aspen HYSYS environment. Companies are able to maximise use of capital and ensure inherently safer designs.

Acid gas cleaning

With increasing focus on unconventional gas and oil in the US, Asia, Saudi Arabia and other regions, acid gas removal, including H2S, CO2 and other contaminants, plays a larger role in hydrocarbon processing and is integral for operation of production units. These stripping processes consume expensive amines and are energy sinks. To assure removal, if the process cannot be modelled accurately, the units must be oversized at a heavy capital and energy use penalty.  

Acid gas cleaning is a new feature in Aspen HYSYS V8.3, which achieves a superior ability to accurately model this problem. In particular, its rigorous rate-based approach and properties ensure the user can predict performance outside of already studied limits. This capability includes a new Property Package, intelligent defaults that make it much simpler to set up these models without being an expert, the unique capability to accurately model packed columns and example files for the most broadly used selections of amine solvents. It models the Acid Gas Cleaning process in HYSYS with unprecedented accuracy. The packing column models, in particular, obviate overdesign with the improved modelling of contaminant removal, including optimal heat stable salt simulation and accurate CO2 predictions minimise equipment fouling to save operating costs.

Moreover, organisations can now model an entire gas processing system, from wellhead to refinery, without leaving Aspen HYSYS. They can avoid transcription errors from manual data transfer and optimise using Aspen HYSYS tools. It is now possible to analyse more configurations than ever before to fit the process’s needs.  

Safety is a priority in every facility. Excess pressure build up in process equipment is one of the most important risk scenarios when a process undergoes an unexpected result (such as power failure). Correct sizing of process equipment and the associated relief systems has long been a key focal point of safe design. When retrofit work is undertaken on plants, existing pressure safety valves are often found to have been under-sized. The lack of pressure relief valve sizing within all of the leading process simulators has long been a headache to conceptual designers during FEED. Correct design of overpressure protection systems is one of the first design hurdles that must be overcome for the process to be deemed feasible. The workflow conducted by many process engineers today is still manual, which limits the number of simulation scenarios that may be evaluated. To address this important engineering need, AspenTech acquired a software product called PSV Plus in October  2012 and has integrated that functionality within Aspen HYSYS V8.3  This new capability brings the ability to solve the overpressure protection design problem within the process modeller’s Aspen HYSYS environment.

Sizing pressure safety valves (PSVs) is a complex process, which requires attention to detail, consideration of all scenarios and liability if not done correctly. The PSV capability in Aspen HYSYS means that engineers can quickly estimate relieving fluid properties and conditions, size the relief valves and produce the required documentation all without leaving the single HYSYS environment. In turn, this design process eliminates errors, improves the quality and significantly speeds up the project work. Aspen HYSYS also allows engineers to rapidly size pressure safety valves for 25 overpressure emergency scenarios by utilising data directly from simulation to perform sizing and obtain fluid properties at relief. Calculations are completed using API 520, 521 standards. Using Aspen HYSYS for relief valve sizing leads to inherently safer design and saves engineers significant time in developing process safety solutions.

Using the PSV functionality integrated into Aspen HYSYS inside the Safety Analysis environment, users can insert PSVs onto process equipment models or singular process streams. General valve parameters can be specified using process data and overpressure protection scenarios can be analysed for each valve, which results in a safe valve size. After sizing a PSV, the proper piping for the valve can be determined according to pressure drop and fluid velocity constraints. Necessary documentation can be completed automatically using the documentation builder feature.

Aspen HYSYS uses process data direct from simulation to size pressure safety valves. Other methods of pressure safety valve sizing require cutting and pasting values from the simulator to external tools. HYSYS accurately models the properties of relief loads, whereas manual methods require approximation of property data or separate Aspen simulations to obtain correct values.

No other simulation software has a direct pressure safety valve sizing tool. Other methods of sizing pressure safety valves do not include line sizing capabilities or automatic documentation of results. Only Aspen HYSYS V8.3 offers a one-stop-shop for completing all tasks pertaining to the design of pressure safety valves.

A truly integrated environment

Across the process industries, companies are faced with global economic challenges, dynamic market conditions and pressure to reduce time-to-market. With continued volatility in hydrocarbon and energy prices, oil and gas producers, refiners, and engineering and construction firms must creatively reduce capital and operating costs, as well as increase engineering efficiency - all in an effort to maximise plant and business performance and profitability.

The process simulation capabilities of engineering optimisation modelling software enables engineers to rapidly evaluate the safest and most profitable designs through quick creation of interactive models for “what-if” studies and sensitivity analysis. These models can be leveraged throughout the plant lifecycle from conceptual to detailed designs, performance rating and optimisation - significantly reducing engineering costs and enabling better operating decisions. In short, integrated conceptual engineering enables the owner and engineer to optimise the design across these many dynamic business and technical criteria.

The single modelling environment in Aspen HYSYS software enables faster optimisation of upstream, midstream and refining processes and improves plant safety. Essentially, with the new industry-first functionalities in Aspen HYSYS, process engineers work more efficiently and more productively by using a single modelling environment. Oil and gas production and processing facilities can be improved to meet a changing set of operating objectives. Existing facilities can be modelled to understand reasons for under-performance and ways to achieve improvements. New facilities can be designed with increased rigour to meet today’s sustainability, safety and profitability goals.  

Ron Beck, Director for Engineering, AspenTech, Reading, Berkshire. UK.

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