(551a) Heavy Oil Reforming in a Dual Circulating Fluidized Bed Reactor | AIChE

(551a) Heavy Oil Reforming in a Dual Circulating Fluidized Bed Reactor


TDA Research Inc. (TDA) has developed, patented, and demonstrated a chemical looping steam reforming process (which we call HyRes – “Hydrogen from Residuum”) that can convert liquid hydrocarbon fuels into syngas from which hydrogen can be extracted. HyRes can generate syngas from a wide variety of feedstocks including JP‑8, gasoline, kerosene, propane, natural gas, heavy oils (including vacuum residuum) and even tar sand bitumen. While it is generally considered impossible to steam reform vacuum residuum without catalyst deactivation, the reason that our process works is because the catalyst is continually regenerated in air to burn off deposited sulfur and coke before too much can build up. All liquid hydrocarbon fuel based reforming operations are prone to severe catalyst coking when using fixed bed steam reforming. The major advantages of our process over fixed bed reforming include: the ability to use waste/dirty fuel sources because of our feed-agnostic reactor design, the catalyst does not degrade because it is continuously regenerated before contaminants build and deactivate it, and the majority of the sulfur in the feed is removed from the syngas product.

When our HyRes process is fully integrated with trace sulfur removal, water gas shift (WGS), and pressure swing absorption (PSA) units, the result is an efficient process to generate purified hydrogen that can utilize a wide range of fuel feedstocks and be scaled for a wide range of applications. TDA is currently contracted by the Department of Defense (Contract # N68335-23-C-0093) to scale-up our HyRes technology to produce 10 kg/day of H2 on a skid-mounted unit capable of being transported between operational sites to generate purified H2 for fuel-cell applications. In this presentation at the 2023 AIChE Annual Meeting, we will discuss the ongoing pilot-scale skid-mounted reformer system, present additional operating data on this technology, and discuss the market opportunities for the technology.

In TDA’s HyRes process, hydrocarbon feedstock and steam are fed to a fluidized bed of Ni-based steam reforming catalyst at 850°C. The hydrocarbons are completely converted into an equilibrium composition product syngas stream. The catalyst is continually transferred to the regenerator, where it is fluidized with air to burn off any coke while the nickel is converted into nickel oxide. In the reforming step, the sulfur in the fuel is removed by the nickel as nickel sulfide (which is burned off in the regenerator and does not enter the hydrogen stream). During regeneration, the catalyst is heated by the oxidation of Ni to NiO. Both Ni oxidation and extra fuel combustion in the regenerator heat the catalyst so that the sensible heat that the catalyst picks up during regeneration supplies energy to the endothermic steam reforming reaction taking place in the reformer. Our catalyst does not deactivate because regeneration removes coke and sulfur from catalyst before they can reach damaging concentrations. Upon returning to the reformer the NiO is reduced back into catalytically active Ni metal by the hydrocarbons in the feed, and steam reforming continues.

TDA’s process for H2 production from fuels uses a commercially available Ni based steam reforming catalyst, but the key to our process is the system design, not the catalyst. The process is based on a dual circulating fluidized bed (DCFB) reactor system, which lets us process dirty, highly coking feedstocks at low steam-to-carbon ratios (low steam-to-carbon ratios improve the energy efficiency of the process). The DCFB reactor design allows for catalyst to continuously flow around the reactor loop while sealing off the gas environments in the reformer and regenerator from each other. By utilizing fluidized bed steam reformers, the sulfur and coke that deposit on the catalyst during reforming forms only a thin film on the surface of the catalyst particles, in contrast to the thick crust of coke that would be formed in a fixed bed, making regeneration easier.

Critically, the sulfur compounds in the feed react with the nickel catalyst in the reformer bed, forming nickel sulfides. Because the sulfur is chemically bonded to the catalyst, the product syngas contains minimal sulfur, which helps keep sulfur out of the downstream H2 purification processes. While the sulfur temporally poisons the catalyst, it is quickly transferred to the regenerator before it becomes irreversibly fouled (the reformer residence time is ~7 minutes, far shorter than the time it would take to poison all the catalyst with sulfur or foul it with coke). We have successfully processed very high-sulfur (up to 3.4 wt.%) heavy feedstocks such as vacuum residuum and HVGO without catalyst deactivation in our DOE Phase II projects. Therefore, in TDA’s HyRes process, the Ni catalysts simultaneously acts as a steam reforming catalyst and sulfur sorbent. As a result, only a small amount of sulfur (<8 ppm H2S) needs to be further removed from the product syngas (using a disposable sorbent) to obtain completely sulfur-free syngas.

The first reactor is the steam reformer (Figure 1, right), where fuel reacts with steam at approximately 850°C to produce syngas (to be subsequently shifted and purified into H2). The heat needed to drive these reactions is provided by the flow of hot catalyst particles from the regenerator. As regenerated catalyst flows into the reformer reactor, used catalyst flows out and is transferred to the regenerator by gravity. A loop seal, which is a nonmechanical valve that transfers solid catalyst particles using aeration gas, facilitates the catalyst flow to the regenerator. The second reactor vessel is a catalyst regenerator (Figure 1, bottom left) where coke and sulfur are burned off in air, which partially reheats the catalyst. The Ni metal in the catalyst is also oxidized to NiO during this step, and this provides the majority of the energy which heats the catalyst. The hot catalyst travels up the riser, is separated by the cyclone, and flows back to the steam reformer where it provides the endothermic heat of reaction. In the reformer, the NiO is reduced back to catalytically active Ni metal by hydrocarbons and syngas, and steam reforming of the fuel resumes. Thus, the sensible heat of the hot catalyst returning from the regenerator to the steam reformer drives the endothermic steam reforming reactions, and in a large unit that is well insulated, allows the process to be autothermal.

This technology was originally developed under a DOE Phase II SBIR project “Hydrogen for Refineries” (Contract DE-FG02-08ER85135), where we demonstrated syngas (CO + H2) generation from extremely heavy high sulfur (2 wt.% = 20,000 ppm) hydrocarbon streams using a single stage reactor. We demonstrated over 500 hours of operation using atmospheric tower bottoms (ATB, b.p. > 650°F) and vacuum tower bottoms (VTB, b.p. > 1050°F) obtained from Valero Energy refineries (both extremely heavy and high sulfur content feedstocks), as well as biomass pyrolysis oil, NorPar 12 (a 50:50 mixture of C11 and C12 alkanes), vacuum gas oil (VGO) and other refined fuels such as JP-8 and methane. We then fabricated and operated a bench-scale DCFB reactor system to demonstrate the continuous reforming and regeneration reactions. Figure 2 shows steam reforming data for heavy vacuum gas oil (HVGO) as the feedstock to the bench-scale HyRes DCFB reactor system. The hydrogen content of the syngas was about 70% on a dry basis, which is typical regardless of the hydrocarbon feedstock because the syngas is essentially at thermodynamic equilibrium at these temperatures (ca. 850°C). Downstream processes such as water gas shift (for increasing the amount of H2 in the syngas) and pressure swing absorption (PSA) purification are well developed technologies that can be added downstream of this reactor system to tailor the syngas to specific applications or purify hydrogen.