MILENA: High-Effiency Gasification
Gasification of biomass and waste opens the full potential of this valuable carbon source. Though combustion is still commonplace, gasification, and specially MILENA, has far more potential.
Gasification of biomass or waste
MILENA is an indirect, fluidized bed gasifier, meaning that product gas is not diluted with N2 from combustion. Solid biomass or waste enters the MILENA in a central riser. A small amount of steam of air is also injected in the riser to fluidize hot bed material. Using the energy of the hot bed material, the biomass or waste reacts into three basic products solids (char), condensable tars, and product gas, comprising mainly H2, CO, CH4, C2H4, CO2, and H2O.
Utilization of residues as energy source
The product gas, char and tars flow upwards into setting chamber, where most of the char and bed material is separated from the product gas. All char and tars are sent to the combustion chamber positioned around the riser. They are then combusted in this second chamber, heating up the bed material before it flows back to the riser, and thus completing the cycle.
Cooling of produced gases
Because of the two reaction zones, MILENA produces a valuable product gas as well as a flue gas. Both gases need to be cooled and cleaned, and separate cooling allows for optimi – zation of efficiency as well as availability. The product gas is cooled by means of air, saturated steam or superheated steam generated in the flue gas cooler. This avoids the presence of cold spots and fouling by tars in the product gas cooler.
Features and benefits
In MILENA the use of a separate combustion zone providing the heat for the pyrolysis results in 100% carbon conversion, boosting gasifier efficiency and minimizing ash volume. The efficiency is further increased as tars and char removed from the product gas are recycled to the MILENA’s combustor reactor where the energy is used for the gasification process.
MILENA delivers product gas with minimal dilution, while using ambient air as oxygen supply for the combustion reactor; pure oxygen supply by an ASU is unnecessary.
The undiluted product gas has a high energy density, typically 17 to 24 MJ/Nm (430 to 620 Btu/scf) depending on the gasified material. This is typically twice the energy density of syngas and three to four times the energy density of conventional gasification
This product gas can be applied in gas engines and gas turbines. For the latter a high energy density is required. The undiluted product gas is also a good basis for downstream conversion to fuels and chemicals.
Gas Cleaning with OLGA
The OLGA tar removal system is based on a conventional multi-stage
scrubber, in which special scrubbing oil is used to rinse tars from
gases. These tars originate from biomass and waste gasification, as
well as coke ovens or underground coal gasification.
Condensation of heavy tars
In the first loop of OLGA, the gas is gently cooled down by scrubbing oil. Heavy tars condense and are collected, after which they are separated from the scrubbing oil and recirculated to the gasifier. The condensation occurs above the water dewpoint of the gas, avoiding the production of contaminated wastewater.
Removal of fines and aerosols
Fine particles and aerosols are removed by the first loop as well by means of a downstream electrostatic precipitator (ESP). The continuous flow of the tar/oil fraction within the ESP removes the captured fine particles, and then the condensed tars and captured solid particles are recirculated to the gasifier.
Absorption of light tars
In the second loop, lighter tars are absorbed by scrubbing oil, thus lowering the tar dewpoint to below 20°C. In this absorber column the oil is saturated by these tars, and this saturated oil is later regenerated in a stripper column. Hot air or steam is used to strip the tar out of the scrubbing oil. Again, tars can be recycled to the gasifier where they are decomposed and contribute to overall energy efficiency
Features and benefits
With the use of OLGA, product gases no longer suffer from tar related problems and can be dewatered, further cleaned if necessary and utilized. Because all captured solids, heavy and light tars are recycled, OLGA is in principle a waste free system. With the special scrubbing oil being re-generated, OLGA has a clear operational benefit compared to conventional biodiesel or rapeseed oil (RME) scrubbing systems.
OLGA only captures tars; it does not change the product gas composition. As such, OLGA enables MILENA to produce a lot of methane, which is the secret of success in the record high efficiency from biomass to renewable natural gas.
OLGA renders tar reduction measures during gasification unnecessary; these measures would otherwise reduce efficiency and energy density. Therefore OLGA enables MILENA to be as efficient as possible. OLGA removes tar at a typical 1% parasitic energy consumption. With the captured tars containing a considerable amount of energy, recycling the tars ensures that this is not wasted but kept in the system and contributing to the energy output of the plant.
Synova Technology supplies a standard, fully-modularized system
called SMM. The SMM system combines the MILENA and OLGA
technologies with downstream water condensation and
scrubbing to deliver clean product gas on specification for
reciprocating gas engines generating heat and power
The basis of the SMM delivery is a detailed design that comprises easy-to-transport modules, sized as 30’ and 40’ containers. The modules are built and tested in the fabrication yard. On site, the plant is then quickly assembled by hoisting the modules in place and connecting the modules. The pre-defined design and the modular construction make this concept an excellent solution for facilities with a small capacity in remote locations.
The MILENA-OLGA technology is highly fuel flexible. A variety of biomass and waste feedstocks can be used to fuel the gasifier. As the SMM is a standard design, built up out of pre-defined modules, the installed capacity of the SMM depends on the fuel quality. The SMM can handle 900 to 1,400 kg/hr fuel with an energy value of 4 to 6 MW. The system can deliver 3 to 4.5 MW (10 to 15 MM Btu/hr) clean product gas to reciprocating gas engines, with which the net electricity supply of this facility will be between 1 and 1.5 MW.
Features and benefits
A fuel flexible power station, converting locally-available biomass and waste with high efficiencies. A pre-designed concept, minimizing the delivery time and simplifying transport as well as on-site construction work, making advanced technology feasible for small scale and remote locations.
The optional zero-water-discharge system purifies and recycles the facilities waste water, minimizing water demand and eliminating a waste water stream.
Producing undiluted product gas, the SMM is also an attractive basis for demonstration facilities that are aiming to produce fuels and chemicals in downstream catalytic and biological processes.
Synova Technology supplies stick-built
MILENA-OLGA facilities. Fed by biomass and/or
waste, these facilities deliver clean product gas
suitable for a gas turbine combined cycle