Q&As about HVO (RD) pretreatment systems

Q: Is it reasonable to expect 1 wppm P in a pretreated feed?

A: Please refer to the table from the HVO supplier’s requirements shared during the webinar. It is possible to reach 1 wppm P or lower for certain feedstocks, but guaranteed  levels most often correspond to the technology supplier’s requirements.


Q: What are the typical materials used for pipes, valves and valve types in the PTU unit?

A: Typical construction materials are 316 or 304 stainless steel.


Q: What is the source of polyethylene in animal fat and used cooking oil (UCO)?

A: Typical sources of polyethylene from animal fats may include items such as ears tags that pass into the rendering process to separate oil from the waste. Another source is the polyethylene packaging material from packaged meat that has passed its last use-by date. Because UCO is an undefined product, there may be residues in UCO from other waste oils.


Q: Is there any fixed-bed solution for the adsorption/bleaching processes that avoids the use of typical filters in this step?

A: A fixed-bed solution is not viable for these processes because it would quickly experience fouling.


Q: Can 90% fatty acid oil be processed using the hydrotreating process?

A: Yes, it is possible. However, due care needs to be exercised with regard to corrosion/metallurgy. This is especially true in retrofit situations where an existing hydrotreater in a smaller refinery is being retrofitted for HVO fuel production. 


Q: What is the catalyst used? How does one treat the spent catalyst to comply with environmental regulations?

A: During pretreatment, no heterogeneous catalyst is in use. However, the addition of acid in the degumming section leads to a homogeneous reaction with organic metal salts such that those become water soluble. When using enzymatic degumming (particularly relevant for soybean oil), the enzymes act as natural catalysts making phosphatides more water soluble. Finally, the adsorbent used in the adsorption section (slurry reactors) has many characteristics of catalysts, such as pore diffusion in and out of the porous adsorbent, competitive surface adsorption, and to some extent chemical reactions on the surface of these commonly acid-activated bleaching clays. You may say that the adsorption sections serve as a guard bed for the HVO catalyst.  Spent adsorption material, with approximately 23-25% residual oil, can be disposed of locally – for instance, to biogas plants. Check with edible oil refineries in your country to determine appropriate disposal outlets.


Q: Is the bleaching earth (BE) recyclable? What is the average consumption of BE, and does the amount of BE required depend on the oil type?

A: No, bleaching earth/adsorbent is not recycled. Consumption can vary from 0.5 to 2wt% relative to the oil flow. Yes, the oil flow does impact consumption. In general, it should be adjusted to the required adsorption duty. Part of the ongoing plant optimization should be to minimize the BE consumption for a given oil quality, always making sure that the pretreated oil quality meets specifications.


Q: How does the removal of metals actually occur?

A: Metals are partially removed through the acid treatment in the degumming section (organic metal salts to inorganic, water-soluble salts). A water wash removes most of those salts, and residual, polar organometallic compounds are removed through adsorption in the adsorption section.


Q: Can you remove organic chloride compounds?

A: Only to a limited extent, according to any differences the organic chloride compounds may have in water solubility and polarity compared to the main fats and oil molecules.   


Q: How do you deal with high free fatty acid (FFA) products like the recovered oil phase from palm oil mill effluent (POME)?

A: There are essentially two ways to deal with FFA products: (1) design the pretreatment plant, particularly the HVO plant with metallurgy that is able to handle such high acidity feedstock, and (2) blend the POME oil with other lower FFA feedstocks before treatment.


Q: Can you treat animal fat (category 1) to HVO or co-processing specs?

A: As category 1 animal fat is classified as a “very high-risk material” due to the risk of TSEs (transmissible spongiform encephalopathies), it is not commonly treated in this way; instead, it is burned directly for heat/electricity production.


Q: Which of the contaminants are more harmful to the HVO process?

A: Of key importance are phosphatides and metals. In general, hydrotreating catalyst can deactivate via two mechanisms: (1) pressure drop, or (2) loss of catalyst activity. Phosphatides tend to cause pressure drop as they build upon on the catalyst particle in the trickle bed reactor. This reduces the void space and creates premature loss of catalyst life. 


Q13: Which specific metals are more relevant and more common?

A: Those would be metals typical for crude fats and oils in the group of Cu, Fe, Mn, Co, Cr, Cd, Ni, and Zn. Occasionally also Pb from external sources. Please refer to  "Determination of some inorganic metals in edible vegetable oils by inductively coupled plasma atomic emission spectroscopy.

Q: Except FFA removal, what are the main differences in plant configuration between pretreatment for biodiesel and pretreatment for HVO?

A: The main difference in plant configuration are the chloride and polyethylene removal sections (if needed) and the bleaching (adsorption) section used in HVO pretreatment plants. The HVO process generally occurs at temperatures above 350°C in a fixed or trickle bed reactor, which means it is much more sensitive to impurities compared to the liquid phase reaction in the fatty acid methyl esters (FAME) process. Pretreatment therefore needs to be finetuned to a higher degree to remove impurities.


Q: Can the chlorine mitigation step also remove organic chlorine?

A: No, not in the chloride removal unit based on a water wash at suitable degree of mixing, residence time, temperature and pH. This phase focuses on removal of inorganic chlorides. To the extent chlorides show the polarity, there can be some removal during the adsorption step, but much depends on the individual organic chloride molecule and the surface properties of the adsorbent.


Q: How do you treat spent adsorbent (general treatment) to meet regulations?

A: In most locations, landfill is not an option. Some plants can deliver the spent adsorbent, which holds about 23% oil and has value as fuel, to cement producers to burn as a support fuel. Furthermore, some companies reclaim the adsorbed oil through solvent extraction as their core business.


Q: What is difference between wet degumming and dry degumming?

A: Wet degumming assumes that gums are separated from the oil by means of centrifuge. Dry degumming is used for oil with low amount of P in crude oil (like palm oil -30...50ppm); removal can therefore be combined with bleaching without having a negative impact on the clay filtration process.


Q: What about removal of bacteria from animal fats?

A: Bacteria is not an issue for feedstock entering HVO pretreatment systems. The HVO processes operate at temperatures above 200°C (392°F) so any bacteria present will die. In any case, bacteria are not an issue in the HVO products (renewable fuels or feedstock to the petrochemical industry).


Q: Will there be fouling issues if a heater is positioned after the degumming reactor? If yes, what is the best method to mitigate these issues?

A: No, fouling issues are not common. A Cleaning-in-Place system can be provided if unusual fouling occurs.


Q: In the degumming step, how does one deal with the variations between different feedstocks in terms of design flexibility, parallel trains, etc.?

A: Please contact us for details because the answer to this question requires a lengthy discussion. Alfa Laval has vast experience in treating feedstocks that vary in composition. I n the case of processing a blend, some suitable average must be applied.


Q: What are the minimum and maximum design capacities of a PTU (speaking of production rate)?

A: The minimum is largely set by the main PTU unit; the high CAPEX demand requires a certain minimum size to be economical, probably about 3000-5000 bpd. There is, in theory, no upper limit because there is a certain capacity for parallel lines. More likely, the upper limit will be set by the feedstock supply chain as well as other logistics and infrastructure.


Q: When phosphoric acid required in an acid mixer? In the adsorption section?

A: Both citric and phosphoric acid can be used in an acid mixer. In some cases, citric acid is preferred due to its chelating capabilities. Additional acid is not added in the adsorption section.


Q: Can you share some ballpark figures on how the OPEX and CAPEX of PTU impacts the overall HVO unit?

A: Please contact us for details. In general, a rough approximation is that the PTU OPEX AND CAPEX would at least be an order of magnitude smaller than the HVO unit, since the HVO unit is operating at high temperature (about 350°C) and high pressure (40-70 bar). The HVO unit also requires associated units such as hydrogen unit, sour gas treatment, etc.


Q: What is the level of organic chloride in UCO? Is it possible to remove organic chloride from UCO?

A: There are not any good representative values for organic chloride in UCO and removing organic chlorides from UCO is only possible to a limited extent (see answer to Q15). Elevated organic chloride levels in a batch of UCO are best dealt with by mixing in the material in low concentrations in a chloride-free feedstock to reduce concentrations so that they fall below the allowable chloride limit in the pretreated feedstock.


Q: What is the typical plot area required for each stage, i.e., chloride mitigation, polyethylene removal, special degumming, and adsorption?

A: Please contact us for details. The plot areas for each stage depends upon the capacity and on how many sections will be included.


Q: Is there a commercial value for gums as biogas feedstock?

A: Yes, there is.


Q: Does Alfa Laval have experience in designing HVO pretreatment units with used cooking oil as its feedstock?

A: Yes, we do. We have some pretreatment units in service and/or are currently designing units that use UCO as feedstock.


Q: What is the main purpose of a centrifugal separator if gums can be adsorbed in the bleaching process?

A: The centrifuge removes the bulk of the impurities, especially any compounds containing phosphorus. If the centrifuge is not used, then the adsorption material consumption and associated oil loss would be prohibitively high.


Q: What is the sulphur reduction percentage after the adsorption? Some feedstock does have high sulphur content?

A: As you may know, CoMo- or NiMo-based hydrotreating catalysts have hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) activity, so normally this is not a critical contaminant.


Q: Does Alfa Laval offer options for spent adsorbent oil extraction?

A: No, Alfa Laval does not, but we can help provide our customers with contacts to such companies.


Q: Can you recommend a process to reduce hexane content in crude palm kernel oil (CPKO) obtained by hexane extraction?

A: We are not sure your question is related to pretreatment for HVO production, but Alfa Laval offers a solution to remove hexane residues effectively by steam stripping under vacuum.


Q: How long does it take to procure all equipment in Alfa Laval’s HVO PTU package? Is there any equipment that will be specified as a long lead item?

A: Please contact us for details. The procurement time is will depend on Incoterms sourcing strategy, plant location, etc. However, in any case, our HVO PTU package has shorter lead times than the main HVO unit (in case such a unit is planned at the same time). Should you require particularly short delivery times if pretreatment is required for an existing hydrotreater in a co-processing scenario, Alfa Laval can tailor sourcing and execution to accommodate shorter delivery times.


Q: How do you handle bacteria removal in animal fats during this process?

A: Bacteria will be removed through the acid treatment and the water wash, and subsequently treated in the filtration section of the adsorption process.


Q: Is the waste filter aid material sent to landfill?

A: Landfill used to be an outlet for waste, but as mentioned previously, many regions no longer permit waste to be sent to landfill. There are several good alternative outlets mentioned in the answer to Q16.


Q: What is the greenhouse gas (GHG) emission ep (emissions for processing) for the Alfa Laval PTU?

A: Please contact us for details. In general, the energy consumption is low because temperature levels are below 100°C and the use of heat recovery/economizing further reduces the energy requirements.


Q: After spent adsorbent extraction, how is the remaining solid waste handled? For instance, for the cases you mentioned in Indonesia or Malaysia?

A: Common outlets for handling solid waste are biogas facilities. Please check outlets in local edible oil refineries in your country.


Q: What challenges do you face when removing chloride, especially in used cooking oil. How much can you reduce the chloride (Cl) concentration?

A: As described, to a large extent, only the inorganic chlorides can be removed. The organic chlorides may be removed, but only to a limited extent. If the resulting chloride content exceeds allowable limits with regard to corrosion, this should be dealt with by mixing the feedstocks, more frequent equipment inspection or other mitigation measures.


Q: What is a typical yield loss (wt%) in the pretreatment unit?

A: Contact us for details. In general, yield loss is at very low and corresponds to the impurities and any moisture removed. There will be some minor oil loss with the gums and with the spent adsorbent (the latter is steamed before discharge to remove oil, almost rendering the spent adsorption dry to the touch).


Q: What about wastewater treatment/evaporation given that the wastewater contains impurities such as metal, chlorides, P, etc.?

A: Here the choice of materials of construction for the wastewater evaporation unit is critical. While material selection is important, we also have a mobile test facility where we can test the evaporation efficiency of your specific wastewater steam.


Q: What are the typical capacities of the PTU in a single train?

A: A single train PTU can be customized, but the size of a single block is 1500 tpd.


Q: Given there are no defined specifications for some feedstocks, do you need to test the feedstock to be able to provide guarantees?

A: For many feedstocks, there are defined specifications (soy, rapeseed oil, tallow, palm oil, distilled corn oil) for UCO, and specifications will be set for design of the unit. Should a feedstock fall outside the design range, processing generally can be handled by blending the feedstock with other feedstock so that the feedstock blend is well below the design specifications for the unit.


Q: We've seen enzyme additions to the pretreatment process of vegetable oils and biodiesel feedstocks have demonstrated lower losses (higher yields) and lower gum volumes.

A: Correct, we have a long list of references for enzymatic deep degumming in pretreatment for fatty acid methyl ester biodiesel, particularly applicable for soybean oil feedstocks. The PLA-type enzymes produce lysophospholipids that are more water soluble and will reduce emulsion. This results in deeper P removal as well as lower oil losses.


Q: I work at a consultancy/design firm and clients usually like to approach multiple PTU suppliers, who would be your competitors in the pretreatment field?

A: There is no supplier who can provide both process know-how and critical equipment for the PTU. In other words, for feedstock flexibility and for future modifications only require a single speaking partner. On top of that, Alfa Laval takes a holistic view of the whole HVO complex, not only the PTU.


Q: What is the maximum capacity of your module (tons, litres/hour)?

A: Contact us for details. As mentioned in the answer of Q40 on capacity, a single train PTU can be customized, but the size of a single block is 1500 tpd.


Q: Big scale, medium scale and small scale?

A: See the answer on capacity above.


Q: Is filter aid or precoating mandatory for treating palm oil?

A: Assuming the worst quality crude palm oil (CPO) is entering the plant, we believe it is highly advisable to use filter aids and precoating.


Q: If 100% CPO is used as feedstock, can the special degumming section be eliminated and instead move directly to the adsorption section? The acid gums collected in the spent adsorbent?

A: Indeed, due to the low phosphorous (P) content in CPO, only the adsorption unit is required.  Although used cooking oil (UCO) also has a low P content, it is not advisable only to have an adsorption section since other impurities may interfere with the adsorption process.


Q: What is the allowable limit for phosphorus (P) in that situation?

A: 30 ppm of P (max 50 ppm) can be used as a limit to determine whether or not to use wet degumming. This limit is also valid for UCO.


Q: If used cooking oil that has P content below 50 ppm, can the special degumming process be eliminated?

A: The gums will be absorbed by bleaching clay and separated by the filter. Therefore, the clay will be used for gums absorption. Removal of methyl ester is the primary task of clay since wet degumming is not too effective here. Therefore, we potentially can use less clay by applying wet degumming, and this clearly has benefits for P > 50 ppm.


Q: Are the antioxidants in CPO still present when treated by the HVO process?

A: No, the final product will be fully hydrogenated, so no antioxidant activity. Natural antioxidants such as carotenes, tocopherols and squalene are usually only present in concentrations of about 500 to1000 ppm so, even if the CPO is not hydrocracked, the fuel properties such as cetane number should not be affected.


Q: What is the additional volume of wastewater required using the HVO process? Per MT CPO feed?

A: The typical additional wastewater used will be in the range of 5–10% of the feed oil flow.