Define product and feed
Authors: Michael Gleeson,  Sean Kelton,  Thomas Considine,  and John Plaxco 
Steward: David Chen, Jian Gong, and Fengqi You
Date Presented: Feb. 2, 2014
A key step in the initial phases of chemical process design is the project definition. Along with the customer definition and location of the facility, the definition of the key feeds and products is a key starting step upon which further decisions are built (Towler, 17). If implementing a new design, key feeds and products should be compared against a similar existing plant or process (Towler, 374). Both feed and product specifications are found in the Design Basis, a non-exhaustive document containing key information and details of the plant and process.
Primary Raw Materials
The definition of raw materials on the Design Basis is located in Section 5 (see image). There are 6 main categories: Feedstock name and grade, MSDS form number, Feedstock availability, Feedstock price, Known feedstock impurities, and Additional specifications. It is of vital importance to recognize that, when deciding upon feed specifications, stoichiometry should be considered, along with safety, yield, and environmental hazards (Biegler, 14). It is important to recognize that the raw materials typically contribute the most to the overall cost of production. Therefore, the choice of raw material can represent an area for optimization and monetary saving. An example Raw Material section of the Design Basis is shown below.
Table 1: Example Raw Materials Section (You, 2015).
|MSDS Form Number|
|Known feedstock impurities||Name, ppm||Name, ppm||Name, ppm||Name, ppm|
Each component of the feed, once decided upon, must be entered in the Design Basis section:
Feedstock name and grade
In this section, the the name of each component of the feed is entered. Along with the generic name of the compound, its formal chemical name, as well as its grade, should be included. No feedstock available in industry will have 100% purity. The most common grade will be "technical" or "industrial". There is also a "laboratory" or "reagent" grade (higher purity), however, it is less common and more expensive.
MSDS form number
The MSDS (material safety data sheet) is an important tool to have when dealing with any material, as it contains key information that can help inform safe decisions regarding the substance. MSDSs contain key physical data about a compound, such as flash point, melting point, boiling point, etc. There is also information on storage and disposal methods. Sources such as Perry's Chemical Engineers' Handbook also contain information about flammability hazards of many chemicals and can be used in conjunction with an MSDS to help decision-making (Seider, 37). In the MSDS form number section, the specific MSDS number of each component must be listed so as to be readily available in case more information is requested.
The availability of each feedstock must be recorded. Feedstock availability can be a determining factor when deciding upon a plant capacity. Generally, the availability and price of the necessary feedstock will depend on site location, and as such, feedstock availability is considered when choosing a plant location (Towler, 506). Whether feedstock availability is recorded on a per year or per day basis depends primarily on the use frequency of each material. This information is dependent on the overall production rate of the facility.
The price of each material is listed in this sub-section. This information is highly relevant when completing the economic analysis. It is important to note that feedstock price is highly dependent on quantity purchased, with larger purchases having a lower cost per unit. Often, quotations for bulk chemical prices must be obtained directly from suppliers after giving them an approximation of how much would be purchased and for how long.
Known feedstock impurities
Along with the general feedstock grade (recorded in the Feedstock name and grade sub-section), the specific known impurities are recorded in this section. The name of each compound (commonly water, minerals, etc.) is recorded along with their concentrations in ppmw. The impurities are listed with the sale of the feedstock product.
Any additional pertinent information about the feedstock is listed in this section. Examples include potential alternatives sources or uses.
The Primary Products are defined in Section 4 for the Design Basis (Please see example image below). There are 6 important subsections that must be completed within the design basis when defining the products: product name and grade, MSDS form number, production rate, product purity, product shipment mode, and additional specifications.
Each individual product that will result from the process, including wastes and side products, must be entered in the primary products section of the Design Basis.
Table 2: Example Primary Products Definition Section (You, 2015).
|MSDS Form Number|
|Product Shipment Mode|
Product Name & Grade
In this section of the design basis, the name of each product formed in the process is entered. First will be the primary desired product followed by any major side products or important waste products formed. Additionally, the desired purity (or grade) of each of these products should be specified. For example, if the product is completely pure, it would be 100% grade. However, if the process creates Hydrochloric Acid in a 30% aqueous solution with water as a stabilizer, then the grade would be 30% and so on. Properly defining side products and wastes is important to allow appropriate decisions to be made for waste processing and for choosing how best to deal with any side products. Typically, grades close to 100% are not attainable without excessive processing and added cost of production. Therefore, lower grades are produced to keep cost of production from inhibiting profit while also still meeting specifications.
MSDS Form Number
It is critical that the MSDS form number for any products be included in the design basis. As previously mentioned, the MSDS contains crucial information about about a substance including, but not limited to, safety/hazards information, actions to take in case of a spill/emergency, first aid measures, storage procedures, and basic material properties. This information is important to the health and safety of employees and must be available for reference at any time throughout the design process. In order to have this information readily accessible, the MSDS form numbers must be included for each product in this section.
For any particular chemical process design, the design team is typically given a specified level of production output from which the level of feedstock input is calculated. In other cases, there is a specified level of inputs available for use. If this is the case, then the production rate should be derived from material balances calculated using the stoichiometry of the reaction(s) or levels of inputs available in any given time period (day, week, year, etc.) multiplied by an efficiency factor. As an alternative, the final production rate can be obtained by looking at the output streams in the stream tables after simulating your process in specialized software (Turton, 24-25).
The rate of product formation should be listed at both a daily and yearly rate, in order to allow for ease of calculations later when computing process economics. The production rate can be listed in other forms as well if they are critical to the design of the plant. For example, if the design problem is given with a desired weekly production rate, then a weekly production rate should be listed here, in addition to a daily and yearly one.
The product purity is the same as the product grade, listed here as a weight percentage (100% is a pure substance), unless additional purity levels are needed, in which case the most pure is listed here (grade then lists the required purity level and each diluted level in addition). The product purity is critical in process formulation in order to define the desired level and efficiency of separation processes needed within the process, which heavily impacts the cost. The product purity will also determine the price at which it can be sold on the market, as well as its potential uses (e.g. high purity laboratory grade chemicals).
Product Shipment Mode
Product shipment mode specifies how the product will be moved from production to distribution centers or customers. This can be largely influenced by the location of the plant. In this section, additional specifications for transport safety as well as handling requirements should be clearly laid out to ensure safe and proper transportation.
In this section, any further pertinent information to the process design or information given within the design statement should be listed. The main purpose of this section is to ensure that the main requirements for the process design are all clearly laid out within one easily referenced document. To that end, information that does not fit in any of the other sections can be placed here.
Case Study 1
As a case study, consider a plant which requires 50,000 tonnes/year of 37% formaldehyde in water (containing 8-12 wt% methanol as a stabilizer). Shown below is the primary products and raw materials definition of this process.
Figure 1: Primary products definition. Taken from Team Born Sinner's (written by Sean Kelton, Michael Gleeson, Thomas Considine and James Xamplas) final report for ChE 351 with J. Cole. Report was submitted on 11/27/13
Figure 2: Raw materials definition. Taken from Team Born Sinner's (written by Sean Kelton, Michael Gleeson, Thomas Considine and James Xamplas) final report for ChE 351 with J. Cole. Report was submitted on 11/27/13
Case Study 2
For a second case study, consider a plant producing 100 MMscfds of hydrogen from methane gas using steam methane reforming. The required feedstock for this process is water and methane. The products are carbon dioxide, carbon monoxide, and hydrogen. The balanced equation for steam methane reforming is shown below:
For this case study, the carbon monoxide is converted to other substances (namely, carbon dioxide, methane, and water) using water-gas shift reactors as well as methanation, so it does not appear in the products section. The raw materials and primary products definition are shown below.
Figure 3: Raw materials definition. Taken from team H-bombs(written by John Plaxco, Vincent Kenny, Spencer Saldana, and Erik Zuehlke) Memo 1 for ChE 352 with professor Fengqi You in winter quarter 2015.
Figure 4: Primary products definition. Taken from team H-bombs(written by John Plaxco, Vincent Kenny, Spencer Saldana, and Erik Zuehlke) Memo 1 for ChE 352 with professor Fengqi You in winter quarter 2015.
Within the Design Basis, the definition and description of both the product and feed streams is of utmost importance. Included in these sections are the names of the components, as well as their prices and key characteristics (i.e., chemical purity and grade, MSDS information, etc.). The product and feed definition is essential in both the initial and final stages of plant and process design as it serves as a starting point for facility design. Additionally, it can be used as a reference for all of the key components in the design.
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5. S. Kelton, M. Gleeson, T. Considine, J. Xamplas, "Evaluation of In-house Formalin Production", ChE 351, 2013