J. Prusha, Emerson, Marshalltown, Iowa
The search to find alternatives to petroleum-based transportation fuels is nothing new. Over the last century, most efforts were a response to availability constraints or high costs. Now, motivations are driven by decarbonization efforts, which require replacing fossil sources with renewables.
Today’s alternative fuel projects evaluate their greenhouse gas (GHG) reduction by determining a carbon intensity (CI) score, calculating all total hydrocarbons consumed—or GHGs released—per unit of energy produced. Numerically, it indicates grams of carbon dioxide (CO2) equivalent per megajoule of energy or fuel produced.
Therefore, the lower the CI score, the better. When all factors are considered, how much does manufacturing and consumption of an alternatively sourced transportation fuel represent a lower CI score vs. conventionally produced crude oil? The following will examine some of today’s options.
Ethanol. Blending ethanol into gasoline is relatively simple, and this technique is used throughout the world to add a renewable component to the fuel, driven by regulations as much as value. Theoretically, ethanol is fully renewable since it can be made from plant sources—including corn, sugar beets and sugar cane—and to a lesser extent from cellulosic waste materials, such as wood chips and crop residues. Still, it gives back some of its CI score savings since fossil fuels are used in its production to plant and harvest crops, along with required distillation processes. The use of food stocks for this purpose has also occasionally disrupted food pricing and distribution.
Diesel. This is a category of its own (FIG. 1) since there are various ways to manufacture fuel that has the basic characteristics of diesel. In the crudest form, some inventive people have modified diesel cars to run on minimally processed restaurant fryer oil.
Economics and environmentalism. In contrast to the past, the global petroleum supply chain has overcome availability issues, and conventional fossil-based fuels are invariably less costly than anything from bio-based sources. Today, motivations for alternative fuels are driven first-and-foremost by environmental considerations, whether by force of direct regulation, incentive programs, or to meet demands from shareholders and the general public.
Incentives include subsidies and tax breaks to launch and maintain these projects, which can help mitigate the additional costs. Some are based on the CI score of the fuel produced, rewarding carbon reduction directly. Incentives vary widely and are often site-specific, so individual companies must examine the possibilities case-by-case.
Critical considerations in this specific industry segment hinge on several key points:
Green diesel production units. The process and its associated equipment are normally designed and constructed under the supervision of a technology licensor, led today by Axens, Topsoe, Honeywell UOP and Neste. A production unit will include the automation hardware and instrumentation necessary to run the process effectively, but instrumentation choices and automation technologies may not be optimized to meet future renewable fuel demands.
Many producers find it necessary to make instrumentation and control system improvements incrementally after the unit is in operation. These add cost initially but provide more in-depth analysis and control, thereby improving process flexibility, decreasing maintenance costs and delivering lower lifecycle costs.
Working on more than 20 new green diesel projects in 2021 alone, the author’s company’s engineers have formulated a growing list of best practices for automating, optimizing and future-proofing these operations, while improving speed to market. Ultimately, the process can become more efficient while reducing the CI score, so fuel produced reduces the overall carbon footprint. The following are a few examples of where operational gains can be made using this approach.
Digital advances. FIG. 2 illustrates areas where digital technologies work in conjunction with advanced instrumentation to provide capabilities that are unlikely to exist in the basic automation system provided with a licensed production unit.
Feedstock flexibility. The risk of multiple feedstocks is that they can have different chemical characteristics and contaminant levels. High corrosiveness can reduce the life of many alloys commonly used for conventional refining, damaging piping, reactors, heat exchangers and control valves.
Refineries that add green diesel production units discover new processing challenges not found in conventional refining:
Ultrasonic thickness sensors measure metal thickness continuously, tracking the advance of corrosion (FIG. 3). Electrical resistance probes measure corrosiveness of the process fluid itself, alerting operators when conditions can cause equipment damage and when corrosion inhibitors should be added. These technologies help producers understand the impact varying feedstocks have on the process.
The reactor section is the most critical unit for maximizing profitability, with reliable and tight control required for smooth operations. Poor control performance can shorten catalyst life and reduce yield, so picking the right control valves is a crucial step in the design process. Digital valve controllers offer advanced diagnostic capabilities able to monitor condition and performance of the entire valve assembly while the valve is actively controlling the process, and this information can be used to improve operations.
Remote proof testing of SIS. Safety instrumented systems (SISs) must be tested periodically to verify their functionality. Usually, these are manual tests and require process shutdowns. Where permitted, partial proof tests reduce interference with operations. Some partial proof test procedures can even be programmed into the control and performed automatically, without the need for a shutdown or even operator intervention.
Asset monitoring. This practice applies a variety of sensor types to monitor the effectiveness and condition of strategic manufacturing assets. Many sensors are wireless and nonintrusive, making them easy to install without waiting for a turnaround. For example, a critical pump should have sensors to measure vibration, bearing temperature, seal-flushing flow and other basic functions. Maintenance managers can see resulting data on an interactive dashboard with warnings when measurements change, suggesting a nascent failure. Similarly, sensors on a heat exchanger can indicate its condition and efficiency, also reporting via a dashboard.
CEMS/PEMS. Combustion processes driving heaters and boilers normally require a continuous emissions monitoring system (CEMS) using flue gas analyzers. In some cases, conventional CEMSs can be augmented or replaced by a predictive emissions monitoring system (PEMS) that uses a process model to calculate pollutant releases based on operating conditions.
Energy balance/information systems. Outside of feedstocks, hydrogen and energy are the largest operating costs for renewable diesel plants. The ability to measure and control energy consumption depends on detailed data and sophisticated analysis for presentation to operators. Here, energy management is fundamental to the very concept and purpose of sustainable fuel manufacturing. Poor energy management reduces any improvement in overall CI score. An artificial intelligence (AI)-based energy management information system (EMIS) can help provide early detection of poor performance, effective performance reporting and support for decision-making.
Mass balance and production optimization. Feedstock variability in this context can be very high. For one year, one plant reported 132 suppliers of 14 different feed types from 362 different locations. So, how does a plant measure how such variability affects process variables? Without effective measurement, reactor control can be nearly impossible. Data from Coriolis flowmeters reflect true mass flow measurements, and this information can be used to ensure proper reactor control is maintained.
The accuracy of the mass flowmeters can be easily verified to ensure plant data is valid.
The author’s company’s Coriolis flowmetersb perform self-diagnostics to verify that their mechanism is working correctly and delivering accurate process data. These online and on-demand verifications simplify calibration without disrupting the process and pulling meters offline to send to a lab for testing.
An additional challenge associated with a changing feedstock mix is understanding operational constraints and identifying optimum operating conditions for each feed type, providing optimum targets and identifying non-optimum conditions. Analytical software can be used to set dynamic operating targets based on conditional operating scenarios. It can also identify operational problems, using equipment readings, alerts and status to generate root cause analysis. This helps deliver product consistency and historical data useful for future feedstock analysis.
Custody transfer validation/verification. Custody transfer—whether fuels and feedstocks are coming in or product going out—is the point where money changes hands. Custody transfer measurement systems (FIG. 4) must provide the best possible measurement accuracy and reliability and comply with commercial and regulatory regulations. This generally calls for Coriolis mass flowmeters with unquestioned accuracy across a wide range, supported by self-verification via internal diagnostics, to prove the flowmeter is functioning correctly regardless of conditions.
Automation of regulatory and tax reporting. Utilizing the best available technologies and systems for custody transfer and mass balance are important components of the regulatory requirements for a renewable diesel plant, but the needs go beyond that. Reports require extensive data from many sources, including point source feed supplier reconciled pathways, contracts, invoices, transportation information and custody transfer documentation, among others.
Data gathering and analysis platforms provide a means to automate data gathering, analysis, visualization and reporting, while having the added flexibility to adapt to future requirements. A central data repository—often referred to as a data lake—stores all types of data required for reports and analytics, with integrated visualization to reduce the labor needed to create highly accurate, yet flexible, reports.
Looking ahead. In the U.S., renewable diesel production is running in third place behind ethanol [averaging approximately 1.2 billion gallons per month (Bgpm)] and biodiesel (averaging approximately 150 MMgpm). Domestic renewable diesel production was at approximately 72 MMgpm in late 2021, but this is nearly double the production from a year earlier. These figures fluctuate from month-to-month, but ethanol and biodiesel imports have matured. Demand for ethanol, under current regulations, is unlikely to increase, and limitations to biodiesel’s practicality suggest it has also reached a plateau.
Globally, the picture is more complex as some countries are pushing for advanced biofuels (made from non-food-based feedstocks such as crop residues), and production coupled with carbon capture and storage. Regardless of how the larger pictured is dissected, the U.S. Energy Information Administration (EIA) calls for growing production capacity with North America remaining the largest market (FIG. 5).
Renewable diesel has enormous room for growth since it can be blended without constraints and used at 100% concentration. It represents a highly practical approach to reduce CI and replace a significant portion of the conventional diesel available today, so its potential is effectively limitless.
Many renewable diesel production units are located on an existing refinery site to take advantage of transport infrastructure and human resources. Some refinery locations have multiple units installed, and others are planning or constructing expansions. To make these projects as effective as possible, engineering teams must examine and consider the improvements possible using the types of digital technologies just discussed. These technologies can be used to maximize efficient use of feedstocks and consumption of fossil fuels during production. When this is done correctly, renewable diesel with the lowest possible CI score can be produced for the greatest effect on carbon reduction.
Any company considering construction of a new unit or an upgrade/expansion of existing capacity should take the time to understand all possible options, evaluate the available digital technologies and select the best ones for maximum operational improvements. Automation is key to developing smart operations, with the flexibility to switch feedstocks as pre-treatment units and associated automation technologies help plants use various feedstocks without damaging existing refinery equipment. HP
NOTES
a Emerson Rosemount™ Wireless Permasense Corrosion Monitoring sensors
b Emerson’s Micro Motion flowmeters
Janelle Prusha is the Refining Industry Manager for Emerson’s flow control products in Marshalltown, Iowa. Prusha graduated from Missouri University of Science and Technology in 2012 with a degree in environmental engineering and from the University of Iowa in 2016 with an MBA.