Raven ($22M for turning waste into hydrogen)

Raven is a clean fuels company that transforms waste – municipal solid waste, organic waste, and methane – into high-quality, clean hydrogen and Fischer-Tropsch synthetic fuels through unique Steam/CO₂ Reforming technology.

Challenge: waste gasification

There is an urgent need to destroy a wide variety of waste streams generated throughout the world and convert the carbonaceous (carbon-based) waste into useful hydrogen-rich syngas. The hydrogen-rich syngas has multiple uses, including the production of renewable H₂ fuel, the reactant gas in a Fischer-Tropsch reactor to produce renewable fuels, and reactant gas in a fuel cell to power the plant.

Any carbonaceous raw material can be converted to syngas through the technological process of gasification. Gasification occurs in a gasifier, a high-temperature/pressure vessel. In the gasifier, oxygen (or air) and steam are directly contacted with the carbonaceous raw materials, triggering a series of chemical reactions that produce syngas.

One problem with gasification is poor conversion accompanied by the release of pollutants into air. The temperatures in the gasifier were not high enough to destroy the complex organic compounds and to prevent the formation of soot and dioxin, even when some of the feedstock was burned with oxygen or air to generate higher temperatures. In addition, combusting part of the feedstock produces CO₂, which dilutes the resulting syngas by decreasing the amount of H₂ produced. In most cases, this combustion is fueled by adding air, which further dilutes the H₂ with nitrogen. As a result, gasification has endured failed applications, poor economics and widespread global criticism as a “incinerator in disguise.”

Raven Technology

Raven has developed steam/CO₂-reforming technology that does not require combustion, oxygen, or the addition of air to the system. The idealized main chemical reaction, which can be considered chemical reduction, involves the combination of hydrocarbon, CO₂, H₂O and heat to produce hydrogen-rich syngas.

Steam/CO₂ reforming reactor

Raven’s high temperature steam/CO₂ reactors use a new method of electrical heating that enables the reactor to reach extremely high temperatures without the use of combustion or oxygen-blown combustion. The reactors can achieve near-complete conversion in the reforming chemistry, resulting in thermodynamic equilibrium composition of hydrogen-rich syngas with little CO₂ or N₂ diluent.

The reactors have various designs.

Figure 1 depicts a cylindrical reactor with a gasket-sealed flange lid on top, a vessel made of fiberglass or other suitable insulation to prevent a burning hazard, and a bottom plate with insulation foam to maintain reasonable temperatures. At the bottom of the reactor is a plurality of concentric tube for feeding the reactor and removing the hot syngas while exchanging between the two, so that the exit syngas is not too hot for downstream piping.

Figure 1: A cylindrical steam reformer reactor. — Figure 1: A cylindrical steam/CO₂ reformer reactor.

A cross sectional illustration of the reactor reveals additional details.

The reactor vessel’s annulus is mounted and welded to the bottom plate. On both sides of the annulus, square wire trips improve heat transfer.

The heating elements are mounted in the top flange. They can be easily removed and pulled out even if they have blisters after service hours. They are inserted downward from the top lid into two flow zones, one with upward flow in the outer annulus and then a flow reversal to downflow in the center of the annulus, with flow exiting the reactor at the bottom. The heating elements have “tension wrap” to increase heat transfer by extending the heat transfer surface.

The inner annular flow region contains 12 heating elements, while the outer annular flow region contains 16 heating elements. The heating elements are powered by busbars located just above the top of the reactor. The total power for all 28 elements is 140 kW. Seven thermocouples are positioned near the heating elements to determine the temperature distribution.

The interior of the reactor is lined with foam ceramic. Additionally, square wire trips are applied to the surface of the insulation foam to increase heat transfer. Note that square wire trips on the surface of foam ceramic and annulus are spaced apart along the flow direction, which provides turbulent mixing with minimal obstruction to the overall flowpath.

During operation, the fed gas enters the reactor through the concentric tubes at the bottom of the reactor. Gas is fed through the exterior of the annulus. As the gas enters the annulus, a screen that generates turbulence to enhance heat transfer is placed there. The gas flows to the top, down to the center and exiting it at the center of the concentric tube.

There are other types of reactors with varying designs of heating systems.

Figure 2 depicts a reactor with a heat exchanger using a reradiating solid body at the bottom. The gas flow enters the bottom of this reactor through a pipe with a tangential entry, which generates a swirling flow in the plenum region to enhance heat transfer on the fins. This inlet flow is preheated by the fins’ heat transfer, which warms the flow entering the reactor’s annular space. The flow flows over the top of this annular tube and down the center. Electrical heating elements further heat the gas, which is enhanced by perforated plate mixer and the turbulence caused by the turbulence-generating features and square wraps on the surface of annular and foam ceramic.

Figure 2: A steam/carbon dioxide reformer with solid body. — Figure 2: A steam/CO₂ with solid body.

As the flow passes over the reradiating body and its base, heat from the flowpath is conducted and convected into a radiating body. The radiating body resides in the reactor exit flow that enters the cylindrical can. At operating conditions, it is a glowing yellow-orange hot surface that radiates and conducts heat onto the surface of the fins. Thus, the reactor exited gas that has been cooled by the reradiating body and the fins leaves this bottom via pipe as a cooled flow.

Figure 3 depicts a reactor with a bottom design for feeding gas to the reactor and extracting the syngas product. The reactant gasses enter the reactor through the flange. The flow from the inlet pipe exit strikes the baffle, where the diverted flow is mixed into small vortices, resulting in a more uniform flow distribution in the bottom plenum box feeding the four annular feed ports producing inlet flows. The product syngas exits the reactor through the single larger port and leaves from the bottom plenum via the pipe containing the smaller pipe inside. This concentric configuration functions as a countercurrent heat exchanger to recover the exit heat and apply it to preheating the feed flow. The flange arrangement allows the gasses in this larger pipe to flow around the elbow and exit through the flange.

Figure 3: A alternative type of steam/carbon dioxide reformer. — Figure 3: An alternative type of steam/CO₂ reformer.

Figure 4 depicts another reactor. The reactor has an entrance tube with a coiled tube heat exchanger with a ceramic reradiating body located at the tube coil center. The extremely hot syngas enters the coil heat exchanger through a port located in this heat exchanger bottom plenum. Long radius elbows are used at the two transition points entering and exiting the coiled heat exchanger. The feed gasses that have been preheated by the coiled heat exchanger enter the annular flow region via a welded long radius elbow. A high alloy annular tube is welded to the base of the reactor that is the top of the heat exchanger plenum. The product gasses exit the bottom plenum through bulkhead fitting and exit piping.

Figure 4: A alternative type of steam/carbon dioxide reformer. — Figure 4: An alternative type of steam/CO₂ reformer.

Steam/CO₂ reforming system

Raven’s steam/CO₂ reforming system produces at least one of H₂ and Fischer Tropsch liquids. The system comprises:

receiving feedstock into an initial reformer;
reforming at least a portion of the feedstock in the initial reformer with steam to produce an input gas, wherein a portion of the input gas is syngas;
transferring the input gas from the initial reformer to a main reformer;
reforming the input gas in the main reformer with steam to increase the amount of syngas;
transferring the syngas from the main reformer to a Fischer Tropsch module;
using the syngas in a Fischer Tropsch reaction;
and extracting from the Fischer Tropsch module H₂O and at least one of Fischer Tropsch liquids generated by the Fischer Tropsch reaction and H₂ generated by the Fischer Tropsch reactions.

Efficient use of steam/CO₂ reforming requires optimized process control parameters and recycling of reaction products to maximize production of hydrogen and Fischer Tropsch products. These process control parameters include controlling steam/CO₂ reforming temperature, addition of steam, CO and, optionally, biogas. Optimization of such parameters has resulted in record H2 production of 50% to 57.3%, removal of sulfur and halogen contaminants, and control of H₂/CO ratio for Fischer-Tropsch.

Increasing the SR temperature only 38 °C. to 871 °C, or addition of biogas can increase H₂ production. Also unexpectedly, for all feedstocks, there was an optimum addition of both steam and CO₂ which would provide a range of H₂/CO ratio from 2.0 to 3.0, with 2.3 being the optimum for FT.

Raven Products

Raven’s steam/CO₂ reformer system turns biomass, municipal solid waste, bio-solids, industrial, sewer and medical waste, and methane into synthetic gas. The synthetic gas contains significantly more hydrogen content than competing technologies, allowing the system to produce more hydrogen and synthetic fuel from the feedstock.

Raven’s syngas prior to additional polishing is already at 2:1 ratio of hydrogen and carbon-monoxide required for Fischer-Tropsch reactors to produce synthetic diesel and synthetic aviation fuels including Jet A, Jet B and milspec JP-8. The synthetic gas can also be converted into emissions-free, 99.999% pure, clean hydrogen.

The Raven’s reformer system offers the best overall economic and environmental benefits for waste generators and processors, while also offering the most favorable economics.

Raven Funding

Raven has raised a total of $21.8M in funding over 4 rounds, including a Seed round, a Venture-Series Unknown round, a Grant round, and a Corporate round. Their latest funding was raised on Feb 28, 2023 from a Corporate round.