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Your most complete professional resource. The American Institute of Chemical Engineers. Kansas City Chapter Technical Article

Featured in 02/01/2007, Issue #5 Newsletter

OSBL Tips for Process Engineers By Karen Bray Many capital projects are divided into two parts, inside the battery limits (ISBL) and outside the battery limits (OSBL). ISBL is typically the process units and the focus of the project, whether it is a grassroots facility or a revamp of an existing unit. OSBL consists of all connections necessary to make ISBL function: feed and product streams, utilities, waste streams, etc. Often times OSBL does not get as much attention as the ISBL during the life of the project. However, it can easily amount to one third of the total project cost or more. Diligently working to minimize the OSBL scope can have a significant impact on overall project cost. Lessons learned from past OSBL projects are presented below to help highlight potential money savings opportunities for process engineers to focus on. 1. Ask questions to learn as much about the ISBL process as possible. On large projects, there may be separate contractors doing the ISBL and OSBL work. The ISBL contractor may not be able (due to proprietary work or other agreements) or may not be willing to share the process with the OSBL contractor. For the sake of overall project cost, the more information that can be shared, the better. As an example, OSBL may be installing new pumps to deliver feed to the unit, and ISBL may also be installing new pumps to raise the feed pressure further. In some cases, one set of pumps might be able to be eliminated, or optimizing the size of the pumps in series could result in a cost savings to the project. A second example is a common case of ISBL utilizing product pumps that have high enough head to require the system to be 300#. Analyzing the overall ISBL-OSBL flow scheme may make it possible to drop to a 150# class system in the OSBL, thereby reducing project cost with the help of a strategically placed relief valve. 2. Define the incoming and outgoing streams as much as possible. Defining the streams will allow for educated decisions on where to pipe the streams to and from. For instance, ISBL may require steam. Delivering 600 psig steam could be overkill if 150 psig would suffice. On one project, ISBL had three vent streams products. The first instinct for OSBL was to pipe them to the front end of the gas recovery (propane and butane) and treatment (H2S removal) unit. Doing so increased the throughput of the unit significantly, triggering upgrades to compressors, exchangers, and other equipment. When the vent stream compositions were defined further, it became evident that two of the three vent streams had no significant propane and butane to recover. Therefore the client was able to save considerable capital by routing those two streams directly to the H2S removal section of the unit.

By Karen Bray

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Your most complete professional resource. The American Institute of Chemical Engineers. Kansas City Chapter Technical Article

Featured in 02/01/2007, Issue #5 Newsletter

3. Spend time with the tank farm personnel when working in an existing facility. The majority of the cost for OSBL often comes from piping and tankage costs. The tank farm personnel are the best resource to help the project understand the flexibility that exists in the current system and are often not included in project planning. There may be out of service piping that can be tested and reused, or simple jumpers that can be made to eliminate new pipe or the need for new tankage. Taking the time to do research on the existing system can potentially save significant money on a project. 4. Define insulation and tracing requirements early in the project. Adding an inch and a half of insulation to a six inch line increases the space occupied by that line on a pipe rack by 50 percent. Missing this insulation on even one line can sometimes cause a complete change in civil/structural scope if there is no longer room to hold it in the rack. Having to add a level or expand a pipe rack size late in a project can be a detriment to both budget and schedule. Tracing in the OSBL can be difficult to define until exact pipe routings are known. There may not be steam in certain areas or even electricity available. Simply assuming steam or electricity is available and applying a factor to pipe length to cover tracing costs early in a project can lead to significantly low estimates. While this is not necessarily a cost-saving tip for OSBL, it is a lesson learned and something that is easily missed in OSBL scope. 5. When working in an existing facility, meet as many people as possible. The ISBL portion of the project is typically located in a well-defined area of a facility, and the link to the rest of the existing facility is the OSBL. It is therefore important that those on the OSBL are good ambassadors for the project. It tends to be those on the OSBL that end up in the existing control rooms, units, and even the cafeteria answering questions about what the new ISBL project is all about. On many projects, especially if it is a grassroots unit, the ISBL will not have a large need to spend time in the existing facility. The better the relationships are between the OSBL and the operators, engineers, and managers of that facility, the better the entire project will likely go. The tips presented above are a few key lessons learned based on past OSBL projects. Many of them may seem straightforward or even obvious, but they can often be forgotten during today’s fast-paced capital projects. Hopefully taking time to think about these things can save your project significant time and money overall. By Karen Bray

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