10.1.4 “Guarantees” for reasonable plant performance
10.4 The process package
The need for a process package, for the implementation of a newly developed process, may seem obvious but, in fact, has not been universally accepted. It is still not used in many projects, and its absence does create many mis- understandings and problems.
The process package is the essential basis for the design of the plant. When working on a large project on many different fronts, important process items should not be decided under the day-to-day pressure of detailed engineer- ing. All the decisions that could affect the new process operation and results should, as far as possible, be included in the process package, after they have been well thought out by all the scientists and managers who participated in the novel process development and in the project definition, and who should therefore be well aware of the possible implications of such decisions. Of course, there will still always be a need for further consultations, but on relatively few specific points.
The content of a typical package, described in detail in Appendix 1, is presented mostly to give an indication of the general scope, and it should be considered as a checklist to be adapted to each specific project. Its main sections are:
• Definition of the “black box” objectives, raw materials, and products • Division into functional sections, as illustrated in a block diagram, with definitions of their function, interconnecting streams, recycles, closed loops, and buffering
• Separate discussions for each of the sections, with the process flow- sheet, the operating variables and the design data used (sources) • Material and heat balances, with any modeling already available
• Major items of equipment — functions, choice, considerations, and preferences
• Services required — options, sources, and costs
• Materials of construction — options, “least expensive but reliable” • Safety aspects
• Disposal of waste streams
The first version of the process package should be prepared and reviewed by the process development group, then approved by the project manager and transmitted to the engineering company, the operating group, and any- body else involved in the project (managers, consultants). Some engineers from the process department of the engineering company may have already participated in the early preparation of the process package, as consultants or service providers.
This key procedure (approval and transmission) is often called the “freezing” of the process for design. Still, this process package will be further revised two or three times during the detailed engineering work, following possible significant decisions, or necessary changes in the equipment or in the control scheme. The process package will be finally completed with the plant’s operating results in the consolidation stage (see Chapter 12).
The bulk of the process package is a compilation of written material from many different sources, which can probably be found in the working files of the different people who participated in the project from the begin- ning. The checklist of a typical package, given in Appendix 1, could serve as a working tool for organizing the compilation of the package. Thus, most of the man-hours in the preparation of the process package are devoted to the orderly organization of all these documents according to a preset sched- ule, leaving clearly indicated space for whatever is still missing. Some editing will probably be needed to make the compiled document as uniform, friendly, and accessible to new users as possible. This can also be an instruc- tive task for new members of the team.
Most of this material should be prepared and reviewed in draft form well in advance, as early as possible before the detailed engineering is begun. Engineering companies usually present to the client’s project manager, in the first few weeks of the contract, all the usual engineering “design criteria” that they propose to use for the different disciplines: civil, mechanical, elec- trical, instrumentation, material handling, etc. The review and approval of all these books takes a lot of time and could well distract the attention of the project management from important decisions on process issues. Advance preparation therefore minimizes the delay in completion of the process package and its approval for distribution.
As described further in Appendix 1, the “black box” representation defines the streams entering the plant (raw materials, streams and services from adja- cent plants, chemicals and additives) and streams exiting the plant (products, waste streams, gaseous emissions). In other words, this is a definition of what is done inside the “black box,” without describing how it is done.
This “black box” is a very useful tool that allows accurate description of the nature and extent of the project to those who need not be bothered with “the technical details,” or outside people who are not allowed into the confidential aspects of the novel process. With the widening of the external front, this tool will be very much in demand from this stage on.
A typical example is illustrated in Figure 10.3, for the process for DAP that was described in Chapter 5, and presented as a block diagram in Figure 5.1. Note that, despite its simplicity, this “black box” representation can also be devised to emphasize the two main “sales points” of the proposed process, which should be appreciated by people operating in this field, namely that:
• Half of the P2O5 used comes from phosphate rock concentrate and hydrochloric acid, and should be much cheaper than in the concen- trated WPA, which constitutes the second half.
• At least some of the impurities in the WPA raw material are also eliminated, resulting in an upgraded DAP product.