Development Stage
4.1 Mini-Plant Objectives and Design
For processes only involving gas and liquid flows mini-plants can be very useful. They cost only a fraction of a pilot plant and can also be quickly modified or cleaned when a problem occurs. A mini-plant typically operates at 0.1 kg/h production rate. Reactions and separations such as distillation can easily be carried out and problems such as foaming or frothing are quickly discovered, especially when the construction material is glass.
In cases where a pilot plant is skipped a mini-plant can reduce potential risks enormously, but then the mini-plant should be a down-scaled version of the commercial scale process design with all unit operations and all recycle flows with the same connections.
4.2 Pilot Plant Objectives and Design
The first question to answer for a pilot plant is: Is it needed? Here are some guidelines to answer this question, derived from Merrow (1991). An integrated pilot plant with all process steps and recycle flows is needed if:
– more than one new process step is involved,
– the process contains one new process step and a complex recycle flow is involved,
– the process contains a novel solids handling step.
– the feedstock is a crude resource, whose composition is not completely known.
Merrow (1991) states that if more than four new process steps are involved, a pilot plant is necessary, but from my experience that is a risky criterion. I have only seen successes when only one new process step was involved.
A process step is novel if new chemistry is involved or a novel piece of equipment is involved, or both. A complex recycle flow is a recycle flow over at least two process units.
If only one new process step is involved, it is not a solids handling step, and if no complex recycle flow is present and no crude feedstock is present, then an integrated pilot plant is not needed. A dedicated mini-test for the novel step only is then sufficient to validate the process design and the process model. Chapter 9 contains a successful commercial scale start-up description of such a case.
The reason that for all other cases an integrated pilot plant is needed is that trace chemical component from the crude feedstock, or formed in the new unit can affect the other unit in an unknown way. A complex recycle flow enhances the build-up of such trace components, often resulting rapid corrosion and fouling.
The second question to answer is: What is the purpose of the pilot plant? In general the purpose of the plant is to validate the commercial scale process concept design and to validate the process flow sheet model. If that is its purpose, then the pilot plant should be a scaled-down version of the commercial scale plant with the same process steps, the same recycle flows and the same conditions. Moreover, sample points at various points in the pilot plant should be made to be able to validate the process model and to see whether build-up of trace components occurs.
Often the purpose of the pilot plant is also to test construction materials on corrosion. To that end also construction material test sections should be built in the pilot plant so that corrosion rates can be determined for various process stream compositions.
Sometimes the purpose of the pilot plant is (also) to provide product samples to customers to test the product performance. This is often the case for products like resins, polymers, paints, processed food and pharmaceuticals (for clinical trials). Often the amount of product for these tests is in the order of 500 kg or more. This then means that the pilot plant capacity has to be large to produce these amounts in a reasonable time. Intimate customer relations are necessary to find out whether these product performance tests will be needed. This means that the marketing department has to be involved at least at the end of the research stage, so that the pilot plant capacity can be determined and its capital and operating cost. Hoyle (2002) provides additional useful information.
The third question to answer is: How to design the pilot plant? The most important part of the answer is that at least an experienced process developer has to be involved in the design, either an employee of the company or an employee from a company with experience in pilot plant designing and construction.
It should not be done by an engineering contracting company who only does commercial scale design and construction. I have noticed several times that such a company gives no priority to the pilot plant design and construction, because for them it is a very small project with little incentives.
As mentioned in this section, the pilot plant should be a scaled-down version of the commercial scale plant, containing all process steps and recycle flows. Because of the high external surface area to volume ratio of the equipment special precautions should be taken to insulate the pilot plant so that it has no cold walls or cold spots.
4.3 Cold-Flow Plant Objectives and Design
For novel process equipment with complex geometries often a so-called cold-flow test unit is constructed in which the fluid flow behaviour of the commercial scale (or near-commercial scale) can be studied. The most used fluid in these tests is water. If a gas–liquid mixture is present in the real process equipment then often air or nitrogen is used as gas and water as liquid. If it is known that the real process mixture shows slow coalescence behaviour then sodium sulphate is sometimes added to the water to reduce the coalescence speed of bubbles. The desired hydrodynamic behaviour, such as rapid mixing of feed streams or plug flow behaviour can then be obtained by modifying the cold-flow geometry until the desired behaviour is obtained. For liquid–liquid systems often water–alkane cold-flow mixtures are used. Here also the droplet formation and droplet coalescence can be very different from the real mixture.
Cold-flow models are also very useful in validating CFD models. By changing geometries and flow rates, the CFD models are validated not only for a single-point solution but also for their trend effects of geometry and flow rate variation. In this way confidence for the large commercial scale process equipment can be obtained.
The limitations of cold-flow models are similar to the limitations of CFD models. For gas–liquid and liquid–liquid systems where bubble or droplet size prediction is essential cold-flow models are of limited use. The reason is that air–water and alkane–water systems have bubble or droplet formation and coalescence behaviour that is different from the real mixture.
4.4 Commercial Scale Process Design in Development Stage
It is of enormous value to make a commercial scale design in the development stage. Only then a scaled-down version of the commercial scale can be designed of the pilot plant. Furthermore by designing for the commercial scale all essential information needed will be discovered.
Commercial scale design is an enormous task. It involves definition of all design details from which all equipment can be procured and subsequently the process can be constructed. In general, manufacturing companies only define the basic design package and the detailed design is made by an engineering contractor firm, who often also does the procurement and plant construction. Guidelines for the commercial scale design are beyond the scope of this book. The reader is referred to Dal Pont (2011) for more information. However, a few elements are crucial for the implementation success and for low cost over its entire life cycle.
First of all it should be designed with its end of life step in mind, even if this is 50 years from the start-up. If so, dismantling is, in general, relatively easy and small costs are involved. If dismantling is not taken into account often soil fouling occurs and the government then charges large sums of money to clean the soil.
Secondly it should have a reliable and complete design base as described below.
4.4.1 Design Base
The design base should be reliable and explicitly described in a document. First of all the document should have a section describing the following points:
– The new elements of the process – An element is new when it is used for the first time for this particular application, even if the technology itself has been used in other applications.
– All essential research and development for scale-up executed and reported as stated in Chapter 3.
Then the design base should be explicitly described. Table 4.1 is a content list of the design base with a brief description. Table 4.1 is obtained from my lifelong experience in the oil and gas and bulk chemicals process industry. But I think it is relevant for all process designs.
Table 4.1
Design Base Content List for Commercial Scale Design at Development Stage
| Content Item | Description |
| Project design name | Unique name to design project, to avoid confusion in communications |
| Location | Information of all relevant aspects of the process location: political, economic, weather, climate, plot size |
| Local operation | Available local operation experience on all organisational levels |
| Industrial environment | In existing industrial complex or ‘green site’ |
| Start-up date | Planned start-up date |
| Safety, health, environment constraints | All local and company constraints for inputs, outputs, operations and storage |
| Required product output | Products’ quality specifications, production rate, flexibility, on-stream time, utilisation factor, lifetime span, major clients and contracts |
| Product storage | Required storage capacity each product and output |
| Other outputs | By-products and effluents: specifications, quantities, destinations (clients, other processes on site) |
| Required inputs | Input specifications and rates of all streams and utilities and list of external and internal company suppliers with delivery capacities and contracts |
| Feedstock storage | Required storage capacity |
| Support required | Required laboratory and analytical support |
| Economic cost and sales | Cost: variable, capital, personnel (fixed) cost, maintenance, sales revenues |
| Safety base | Runaway behaviour determined and safety mitigation measures |
| Health base | Health hazards and mitigation measures for all process components |
| Environment | All streams and potential environmental streams and mitigation measures |
| Social acceptance | Social acceptance determination of process and products |
| Research and development quality base | Scale-up validation, physical and chemical properties quality |
| Lessons learned | Lessons learned from the same or similar existing processes or from other processes at same location or country |
| Process description | Process block flow diagram with all inputs/outputs, technologies, special conditions (temperature, pressure). Operation: batch/continuous |
| Process operation | Type of control and quality operational personnel required |
| Essential requirements | All elements for feasible, reliable design and operation |
| Special equipment | Novel, special, auxiliaries |
| Feasibility assessment | Economic, safety, health, environmental, social and technical |
Table 4.2 shows phenomena critical to scale-up. This table can be used to determine which process sections of the process are critical to scale-up.
Table 4.2
Checklist for Phenomena Critical to Scale-Up
| Phenomenon | Locations to Check |
| Fouling | Heat exchangers, catalyst beds, top and bottom distillation columns, liquid–liquid settlers |
| Corrosion | Trace chemicals build-up in recycle flows, heat exchangers, dead zones in combination with fouling |
| Erosion | Tube bends, vessel outlets, solids/fluids operations |
| Foaming | Gas–liquid systems, distillation, bubble columns |
| Bubble formation | Gas–liquid systems large-scale eddy hydrodynamics |
| Droplet formation | Liquid–liquid systems |
| Mixing | Reactors |
| Residence time distribution | Reactors, gas–liquid absorbers |
| Mass transfer | Reactors |
| Heat transfer | Reactors |
| Impulse transfer | Packed bed reactors, micro-reactors |
Table 4.3 is a checklist as to when a novel process technology is to be purchased. It is based on the author’s experiences and no claim is made that this checklist is complete.
Table 4.3
Checklist for Purchasing Novel Processes
| Check Item | Background |
| The process has been pilot plant tested | The word ‘pilot plant’ is easily used. Find out what really has been tested or used |
| The pilot plant is an integrated down-scaled version of the commercial design | Often only a pilot plant is available and not a commercial scale design |
| New equipment items | An equipment is new if it has not been used for the specific process application |
| Characteristic time pilot plant same as commercial scale | Has pilot plant same time scales as commercial scale, or are time effects by hold-ups different? |
| Components composition in every stream | Have all pilot plant streams been analysed for component build-up? |
The overall quality of the final detailed process design, the purchasing of equipment, the construction and erection of the plant determines of course the final reliability of the process. A description of detailed measures to ensure this is beyond the scope of this book. Involving an engineering contractor experienced in the specific process is a key factor for success. If the process is very novel, then an engineering and procurement contractor experienced in processes involving similar products and streams should be searched for. If that is not possible then at least an engineering contractor experienced in processes of the industrial branch should be searched for.
4.5 Development Gate Decision
4.5.1 Risk Mitigation
If the innovation involves a new market, a new product, new chemistry and new process technology, the risk will be very high. This risk can be reduced for instance by first entering the new market with an existing product or vice versa entering an existing market with the new product. It can also be reduced if it involves new chemistry and new process technology, to choose conventional process technology in combination with the new chemistry.
External experts on the new risk types can be invited to comment on the development results and the plan to go to commercial scale operation. It can be experts on the new market, or on product performance, or on chemistry or on process technology.