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Paper for the IAPG Natural Gas Treatment Congress Neuquén, Argentina - October 17-20, 2004

Advanced Operator Training and Plant Operations for a Gas-Plant using First Principles Dynamic modeling and Human-Machine

Interface Emulation

Rajeev Agarwal – Soteica, Vancouver, Ky Alston and Thomas J. Oliver -- BP Rockies Unit, Painter Complex, Evanston, Juan Pablo Ruiz and Sebastian Cuneo – Soteica Latinoamérica (sebastian.cuneo@soteica.com – P: +54 11 45555703).

Abstract

The BP, Painter Gas plant located in Evanston, Wyoming needed an operator trainer to refresh the skills of the existing operators and to train younger operators. At the same time, it was recognized that a first principles based dynamic process simulation of the plant would result in improved operations and profitability. It was therefore decided to create a first-principles dynamic model of the gas plant and to couple this model with an emulation of the Human-Machine interface. The HMI was emulated using Intouch from WonderWare and the detailed process model and control logic was implemented using HYSYS Dynamics software from Aspentech. The communication between the various software pieces, as well as the operator evaluation is managed by S-OTS, a supervisory software developed by Soteica. The OTS allows for training with and without an instructor and also allows for automatic evaluation of operator performance. The operator trainer is in the process of being deployed. The training system offers the operators a realistic training environment where the model predicts performance during upset conditions, particularly startups and shutdowns. The model will also be used for process studies and to help operators better manage unexpected faults and upsets.

Introduction The Painter Asset consists of the Painter and East Painter reservoirs, approximately 15 miles NE of Evanston Wyoming. In a unique agreement, Chevron USA operates the field production and injection facilities, while BP operates the gas plant. Painter Reservoir Unit The Painter Reservoir Field was discovered in 1977 and East Painter Reservoir Field was discovered in 1979. Hydrocarbons from both fields are trapped by northeast-southwest trending, doubly-plunging asymmetric anticlines in the hanging wall near the leading edge of Absarko Thrust. These high-relief anticlines allow structural closure and

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hydrocarbon columns of approximately 1,150 feet at Painter Reservoir Field and 1,400 feet at East Painter Reservoir Field. Painter Reservoir and East Painter Reservoir Fields are two of a series of oil condensate fields producing from the Jurassic Nugget Sandstone Formation. The reservoirs contain volatile oil rims with retrograde condensate gas caps. Nitrogen has been injected into both reservoirs to maintain pressure and maximize recovery. Nitrogen injection was initiated in 1984 and discontinued in the Painter A field in November 2000. The East Painter field is still under full pressure maintenance, while the Painter field is now in full field blow down. East Painter has a current inlet rate of 210 MMscfd and 69% N2. Painter A field has an inlet rate of 27 MMscfd with 73% N2. Currently there are 26 producing wells in the Painter A field. There are also 21 producing wells and 8 injection wells in the East Painter field. PCGP Plant The Painter Complex Gas Plant, PCGP, provides N2 removal and NGL recovery from the produced gas. PCGP has a current capacity of 265 MMscfd. The facility was constructed at an approximate cost of $107 MM and has been in operations since 1987. In Addition to Painter A and East Painter, PCGP, historically, has processed gas from 3 other fields including Clear Creek, Ryckman Creek and Anschutz. At PCGP, the first step is inlet separation of gas and liquids from the fields (see simplified Painter block flow diagram). The gas is first chilled using propane refrigerant (3 - 3,500 HP compressors) and then pre-treated before the NGL/NRU trains. Inlet and chiller liquids are stabilized in a two-tower stabilizer that produces a stabilized condensate and NGL product. Gas pre-treatment consists of an amine system using DEA (diethanol amine) to remove carbon dioxide, a TEG (triethylene glycol) dehydrations system for bulk water removal, sulfur impregnated carbon beds for mercury removal, and molecular sieve for final dehydration. Portions of the cold boxes consist of braised aluminum plate-fin exchangers and aluminum piping, which can be damaged by the parts per billion levels of mercury in the gas. Water and carbon dioxide can freeze at the cryogenic temperatures found in the NGL/NRU process. NGL NRU Process Gas from the pre-treatment systems is split between two NGL/NRU cold box trains. The gas is cooled in the NGL section of the process to about –135 F using cold sales gas and nitrogen from the NRU as well as propane refrigeration and turbo expander. Liquids in the NGL section are sent to the demethanizer column where a pipeline NGL product is

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produced. The column and NGL section of the process can be operated for ethane recovery, ethane rejection, and dew point control recovery of NGL. Gas from the NGL section is further cooled and fractionated in the NRU column to make an overhead nitrogen gas and what is essentially a liquefied natural gas (LNG) product off the bottom of the column. The liquid from the bottom of the NRU revaporizes as it is returned through heat exchange. The NRU column operates at about –245 F overhead and –160 F bottoms temperatures, far colder than traditional NGL recovery. Energy for the nitrogen-methane separation is provided by a methane heat pump system (3 - 7,500 HP Compressors), which provides heat to the bottom of the NRU column and refrigeration to the NRU column condensers. The methane heat pump fluid is manufactured on-site using a small distillation column integrated within the NRU process (make-up system) and consists of very high purity Methane (>99.7% pure CH4). Essentially all of the heat pump fluid is liquefied and then revaporized in this process, and a small amount of this stream is drawn-off as an LNG product and sold via truck sales to regional customers. Plant capacity for LNG is 40,000 gallons per day and is limited by refrigeration and heat pump fluid make-up capacity. Sales gas and nitrogen products are compressed in the residue/nitrogen compressors (dual service machines), to a pressure of about 1,000 psi. Sales gas production from the Painter Units is sold via the Kern River Pipeline and Questar Pipeline Systems. Nitrogen product gas is sent to the injections compressors and pressure increased to 4,900 psi, for use in the East Painter Field.

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Injection Compression East Painter Compression is operated by Chevron. It takes low-pressure nitrogen at about 900 to 1050 psig and compresses it to 4,800 psi for injection into East Painter. East Painter Compression includes three engine driven machines with a maximum capacity of 35 MMscfd and one 50 MMscfd electric driven injection compressor. There is also low-pressure inlet compression located at East Painter Compression. Inlet Compression Reservoir pressure maintenance was discontinued in the Painter field in November of 2000. Inlet Compression for the Painter reservoir started up on September 24th of 2001. One of the existing PCGP Res/N2 compressors was converted to Inlet Compression service, with a capacity of 13 MMscfd to 98 MMscfd and a design inlet operating pressure down to 100 psi.

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Control System

The DCS at PCGP is Fisher Provox OWP.

Operator Training Approach

The responsibility of this operator training project was given to senior operators by the PCGP management and wide latitude was given to them in defining the model and the deliverables for this operator trainer. The senior operators decided that the best use of the OTS would be to train in upset conditions, particularly start-up and shutdown. They also wanted the OTS to operate faster than real time. The idea here is to provide the operators with the ability to anticipate upcoming process upsets. It should be pointed out that is approach to “faster than real time” operator training is only one of two possible approaches. Most operator training is done in real time to give operators a feel for the real time behavior of the process. However, in this it was deemed more important to train operators in anticipating upcoming process upsets. One implication of “faster than real time” training is that real DCS hardware or emulation (in this case Fisher Provox OWP) cannot be used. DCS hardware (or emulation) works in real time and cannot go faster than real time. In order to accomplish this goal of “faster than real time” training the following needed to be done:

1. The control system including controllers, digital logic and alarms had to be modeled inside HYSYS.Dynamics

2. The Fisher Provox OWP Human Machine Interface (HMI) was emulated. In this case Intouch from Wonderware was selected as the screen emulator.

3. The amount of control logic and alarms modeled were restricted to the absolute minimum essential for the training scenarios that the senior operators had in mind.

4. The complete plant model (as one single model) was running at 2.5 times real time on the selected hardware. This model was broken up into smaller models to speed it up even more.

5. A supervisory software (S-OTS) to communicate between HYSYS.Dynamics and the Intouch interface had to be developed.

Modeling Approach

Since HYSYS.Dynamics is a first principles based process modeling software it re-produces plant behavior, once the correct equipment parameters have been entered into the model. One great advantage of first principles models which are based on rigorous thermodynamic models is that the model reproduces actual plant behavior essentially out-of-the box. Once the model is built, only minor tweaking is necessary to match plant data. Actual plant pressures, temperatures, flows, pressure drops and heat duties were matched with great accuracy.

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The model development was a joint effort between Soteica and the Painter operators. Soteica provided technology transfer in modeling know-how in the use of HYSYS and the operators provide their invaluable insight into the real plant behavior. Of equal importance is the experience of the senior operators in focusing on specific areas of plant upset conditions that would provide the maximum training benefit meant that the model was tailored to those training scenarios. This resulted in a streamlined model with focus on those aspects of the physical plant that were necessary for the training scenarios. The HYSYS virtual plant models consist of all the major parts of the plant. These are: Inlet separation, DeEthanizer, Stabilizer, Recompression, CO2 removal using DEA, dehydration using TEG, and the NRU/NGL (aka “cold box”). The original model was developed in independent sections for maintainability and parallel development. These sub-sections were integrated into one large model. This large model runs at about 2.5 times faster than real time on the chosen hardware. However, this speed-up is not considered to be enough for the specific anticipatory start-up scenarios for operator training. The model is currently being split into smaller sub sections for faster simulation time and parallel training on different parts of the plant.

Human-Machine Interface (HMI) Emulation It was decided very early in the life of this project that the HMI would be emulated using Intouch from Wonderware. Actual Fisher Provox OWP HMI screen files were taken and translated to Intouch screens. This resulted in an HMI emulation that is virtually identical to the real Fisher Provox OWP HMI. As mentioned above not all the details of the control system were modeled with most of the missing functionality in the number of alarms modeled. Only the important ones were modeled. Another aim of the project was to provide a place where operators could come and refresh their skills even in the absence of a human instructor. To achieve this, the S-OTS supervisory software provides for a simple launch button for the OTS. S-OTS also provides for automated pre-programmed upsets for the training session. Finally, operator performance statistics can be obtained by defining upper and lower acceptable band on key process variables.

Virtual Plant Model, HMI Communication

The communication between the HYSYS virtual plant model and the Intouch HMI is provided using COM technology and the Intouch API. This communication software, which constitutes part of Soteica's solution "S-OTS", was a large part of the development work for this OTS project.

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The communication has to be efficient, since hundreds of tags (analog and digital) are going out of the virtual plant model and control signals are coming back in. Control signals include controller states, set points and outputs set by the operator on the HMI. They also include digital switches such as pump on-offs. An attempt had been make in the early phase of this project to communicate between the plant model and Intouch using DDE. This technology was not a practical way for communicating large amount of tag data that is a necessary part of any realistic OTS project. The figure below shows some screen shots of the HYSYS virtual plant model and the Intouch HMI.

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Main Training Scenarios The two main training scenarios for this OTS project are start-up and shutdown. The senior operators at the Painter complex identified that the startup-time could vary between eight hours and four days depending on the experience of the operators in the control room and subsequent upsets occurring during start-up. It is therefore obvious that

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the maximum benefit from operator training would come from familiarizing the operators with the start-up procedures. Painter has written start-up procedures, however “hands on” training of actually going through a start-up seems to be a much better teaching method. The “faster than real time” environment is there to give the trainees practice in anticipating the changes and upsets that will come their way as the plant starts up and shuts down.

Summary The main objective of this project is to train operators of the Painter complex in a faster than real time environment to anticipate start up and shut down process upsets. At the time of writing this paper most of the major work on this project is complete and the model is undergoing modifications to make it run faster. It is currently running 2.5 times faster than real time. The supervisory software developed to communicate between the virtual plant and the emulated HMI is extremely efficient and is not a contributing factor to the OTS model speed. The approach of using Intouch to emulate the HMI can also be considered a success as it provides for the trainee the same “look and feel” as the Fisher Provox OWP HMI. The trainees will face a training environment that will provide pre-programmed upsets and most importantly allow them to practice start-ups and shutdowns. Significant improvements in start-up time are expected (see above).