This draft or learning was prepared by me to design an algae reactor that are focused on carbon capture usage, not biomass production. So, it will focused on how can this reactor being used to capture carbon and how to optimize it. Even this project mentioned about biomass production or biomass productivity of microalgae, this reports are not specifically designed to do so.
Process Thinking Fundamentals
Here, I’m starting with the basic fundamentals of the process design like design basis, system boundaries, mass balance between inputs and outputs, accumulation or steady state system, and also system development life cycle.
The output of this process thinking fundamentals are the Generic Reactor Box Maps or so called Hubka-Eder map that heavily focused on mass balance between inputs and outputs.
Carbon Dioxide as Process Feed (Input)
At this stage, I’ll learn about how to treat carbon dioxide as a material, not as just symbol in an equation. It will talk about the concentration, gas flow rate and pressure, material phase (liquid and gas phase of carbon dioxide), and the most important thing is the difference between available CO₂ are not the same with useable CO₂.
The output of this stage is to be able to map CO₂ concentration in each phase. How much the input and how much that are dissolved in the medium or being transferred to the medium. Second, how much of the dissolved CO₂ are being fixed by the microalgae and how much of it that are released by the reactor exhaust.
Photosynthesis for Engineer
Photosynthesis is the basic of microalgae-based carbon capture. This stage will breakdown it processes on how carbon is fixed by microalgae through photosynthesis. It will talk about photosynthesis variable such as light intensity, Oxygen concentration as inhibitory product, and the saturation concentration. This was matter because light is the main rate limiter.
The output of this stage is adding light intensity as the input variables and oxygen as the output variables and highlighting that the overall process is light-driven, not feed-driven process.
Gas-Liquid Fundamentals
At this stage, the learning will be focused on the mechanisms of gas-liquid transfer such as dissolutions rate, bubble size, retention time, gas stripping or accumulation, and also transfer rate.
The output of this stage is mapping the CO₂ source, sparging system, how much is the unused CO₂ and labeling where the losses happen.
Reactor Geometry Logic
The reactor geometry should be perfectly or well-designed, because it’s basically the place that facilitate the whole carbon capture process. The geometry aspect that should be calculated well is the height to diameter ratio or surface to volume ratio. Also, there’s a lot of reactor configuration that need to be consider from flat-panel, tubular, or column reactor.
The output of this stage is choosing one type of reactor and explained why it helps the CO₂ fixation process along with the technical challenge that comes with it.
Control Thinking
For this stage, we are going to focus more on things that need to be controlled, drift, and why algae systems oscillate. The terms oscillate here are refers to the oscillating data log of microalgae and why it happen and how to control it.
The output of this stage is list of items that need to be controlled and kept being stable. But it limited and not including the instruments yet.
Design Basis
This is the first real milestone. This is basically a compilation of the last 6 stages. Here, we are going to learn on how to convert an assumptions into a engineering basis fundamentals and how uncertainty is handled.
The output of this stage is a purposes of the project, CO₂ source assumption, fixation target, reactor type, operating mode, and the boundaries of the projects. Basically this is the design basis for the photobioreactor unit.
Block Flow Diagram (BFD)
The block flow diagram is a simple flow diagram that help us map the whole end to end process. Here we are going to learn about the process sequencing and what belongs, what doesn’t.
The output is the BFD itself, containing the CO₂ in, light in, PBR setup, CO₂ out, biomass bleed, and also the utilities. This stage is limited to the terms first, so there’s no calculation numbers yet, just a clean logic.
Process Flow Diagram (PFD)
This is a compilation of the whole steps before. This stage is about translating basic logical thinking into an engineering communications. It’s more like a capstone PFD.
This is where we gather information related to each of the 9 steps before. The mapping done by asking a right questions at each steps along with the answers, then convert the answer into a knowledge base, then use the knowledge to make a decision or choices. The succession of this stage is when I Stop asking “What should I include?", Start saying “This thing doesn’t belong here” and The diagram get simpler, not more complex.
Questions Strategy
This questions mapping is a steps to map primary and follow up questions related to each steps. And here, we are going to breakdown the questions that need to be answered first before stepping into the next learning phase.
Here’s what I should know about asking the “right” questions.
Three properties of Good Engineering Questions
5 Questions Lenses
This is a basic 5 lenses to generate a right questions for each steps:
Master Questions Formula
Use this sentences:
“What must I understand about ___ so that I can decide ___ without needing to design the whole plant?”
If the questions need the whole plant to answer it, it’s too early to ask. We are still in the fundamentals step
Example
Bad Questions:
Too broad and no decision-force here
Good Questions:
It’s good before it define variables, and leads to force-decision making
Questions and Answers
Stage 1: Process Fundamentals
“If I skip this steps, my design will fail because I don’t know what information that must be fixed before drawing a process diagram”
so the main questions must be:
“What information must be fixed in order to represent any process as a bounded system with defined inputs and output?”
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Answer
The information that should be fixed is system boundary, inputs and outputs, accumulation assumptions, and purposes of the system.
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And the sub-questions should be:
Stage 2: CO₂ as Process Feed