Pilot Scale Plant

[Shane Rouse]

Apilot plant is a pre-commercial production system that employs new production technology and/or produces small volumes of new technology-based products, mainly for the purpose of learning about the new technology. The knowledge obtained is then used for design of full-scale production systems and commercial products, as well as for identification of further research objectives and support of investment decisions. Other (non-technical) purposes include gaining public support for new technologies and questioning government regulations.[1] Pilot plant is a relative term in the sense that pilot plants are typically smaller than full-scale production plants, but are built in a range of sizes. Also, as pilot plants are intended for learning, they typically are more flexible, possibly at the expense of economy. Some pilot plants are built in laboratories using stock lab equipment, while others require substantial engineering efforts, cost millions of dollars, and are custom-assembled and fabricated from process equipment, instrumentation and piping. They can also be used to train personnel for a full-scale plant. Pilot plants tend to be smaller compared to demonstration plants.

A word similar to pilot plant is pilot line.[2] Essentially, pilot plants and pilot lines perform the same functions, but 'pilot plant' is used in the context of (bio)chemical and advanced materials production systems, whereas 'pilot line' is used for new technology in general. The term 'kilo lab' is also used for small pilot plants referring to the expected output quantities.[3]

If a system is well defined and the engineering parameters are known, pilot plants are not used. For instance, a business that wants to expand production capacity by building a new plant that does the same thing as an existing plant may choose to not use a pilot plant.

Additionally, advances in process simulation on computers have increased the confidence of process designers and reduced the need for pilot plants. However, they are still used as even state-of-the-art simulation cannot accurately predict the behavior of complex systems.

As a system increases in size, system properties that depend on quantity of matter (with extensive properties) may change. The surface area to liquid ratio in a chemical plant is a good example of such a property. On a small chemical scale, in a flask, say, there is a relatively large surface area to liquid ratio. However, if the reaction in question is scaled up to fit in a 500-gallon tank, the surface area to liquid ratio becomes much smaller. As a result of this difference in surface area to liquid ratio, the exact nature of the thermodynamics and the reaction kinetics of the process change in a non-linear fashion. This is why a reaction in a beaker can behave vastly differently from the same reaction in a large-scale production process.

After data has been collected from operation of a pilot plant, a larger production-scale facility may be built. Alternatively, a demonstration plant, which is typically bigger than a pilot plant, but smaller than a full-scale production plant, may be built to demonstrate the commercial feasibility of the process. Businesses sometimes continue to operate the pilot plant in order to test ideas for new products, new feedstocks, or different operating conditions. Alternatively, they may be operated as production facilities, augmenting production from the main plant.

The differences between bench scale, pilot scale and demonstration scale are strongly influenced by industry and application. Some industries use pilot plant and demonstration plant interchangeably. Some pilot plants are built as portable modules that can be easily transported as a contained unit.

For continuous processes, in the petroleum industry for example, bench scale systems are typically microreactor or CSTR systems with less than 1000 mL of catalyst, studying reactions and/or separations on a once-through basis. Pilot plants will typically have reactors with catalyst volume between 1 and 100 litres, and will often incorporate product separation and gas/liquid recycle with the goal of closing the mass balance. Demonstration plants, also referred to as semi-works plants, will study the viability of the process on a pre-commercial scale, with typical catalyst volumes in the 100 - 1000 litre range. The design of a demonstration scale plant for a continuous process will closely resemble that of the anticipated future commercial plant, albeit at a much lower throughput, and its goal is to study catalyst performance and operating lifetime over an extended period, while generating significant quantities of product for market testing.

In the development of new processes, the design and operation of the pilot and demonstration plant will often run in parallel with the design of the future commercial plant, and the results from pilot testing programs are key to optimizing the commercial plant flowsheet. It is common in cases where process technology has been successfully implemented that the savings at the commercial scale resulting from pilot testing will significantly outweigh the cost of the pilot plant itself.

Custom pilot plants are commonly designed either for research or commercial purposes. They can range in size from a small system with no automation and low flow, to a highly automated system producing relatively large amounts of products in a day. No matter the size, the steps to designing and fabricating a working pilot plant are the same. They are:

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When developing or applying a new process or energy technology it is generally accepted best practice to build a pilot plant to test the technology and demonstrate that it works before building a full scale plant. It is intuitive that if mistakes are made in the design of a pilot plant, the pilot plant may fail. What is not so obvious is that certain mistakes in the design of the pilot plant can allow the pilot to work well, but cause the full scale plant that is built afterwards to fail.

My intent for this article is to outline key questions that need to be considered when designing a pilot plant, in order to ensure that promising technologies are given a fair trial and that the money invested in them is not wasted. Although it is primarily technical in nature there will be value for senior management and investors to read the Reasons for Piloting and Compromise Considerations sections so that they can ask the right questions and protect their investments.

All of these reasons can be summarized by the concept of demonstrating: whether to an investor, a potential customer or yourself, you are proving that it works at a given size and in a given set of circumstances. However, in all of these cases there is a critical, unspoken assumption: if everything works you are going to want to build a bigger, often full-scale, plant. In order to build the bigger plant, you are going to have to collect from the pilot plant the data required in order to design that larger plant, and in order to do this you have to have designed the pilot to be able to provide that data. Thus, the reasons for building a pilot plant should be summarized into two requirements:

With an understanding of these general reasons in mind, the following sections will explore some of the important considerations for designing a pilot plant. The sections are divided by consideration (Demonstration and Engineering Data) although each consideration clearly impacts the other.

When looking at how to design a pilot for demonstration purposes, the first questions to ask are who is the audience for the demonstration and what are they really looking for. Understanding the answers to these two questions will help you ensure that design criteria are picked intentionally and not randomly.

Beyond the whim of a client or senior executive, there are many factors to consider when deciding how big to make your pilot plant before even considering the engineering data requirements. The most obvious of these is flow rate. Is there a standard flow rate that is used for piloting in this industry? Are there other pilot plants that this plant may be installed up or downstream of? Is the product of the plant going to be used for some sort of bulk testing and if so how much is required and how quickly?

A common request for a demonstration plant is to have it mobile or transportable so that it can be tested with various feedstocks without the (sometimes impossible) necessity to transport the feedstocks to the plant. For a fully mobile plant this is typically done by mounting it in a wheeled trailer or in a shipping container, while transportable plants are generally done in multiple shipping containers or skids that can be bolted together at site. The benefits of being able to do this are fairly obvious, but it can significantly increase the cost (in some cases by a factor of 2 or more) so make sure that this is a need to have and not a nice to have: are there multiple destinations confirmed or is it just a concept? I have been involved with more than one mobile pilot plant that was used in a single location, put in storage for a period of time, and then disposed of.

Going back to the question of what is the audience really looking for, it is worth asking whether the entire process needs to be demonstrated, or just one or two unit operations. If this is a case where the vast majority of the proposed process is known technology and there are only a few elements that need to be demonstrated, a lot of money can be saved by piloting only the unit operations in question. Frequently this can be done by placing the pilot unit operations in parallel with an existing process and treating a slip stream. If not, you may need to synthesize the feed to the unit operations, so make sure that this is acceptable to the audience.

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