The biomass is loaded and stored in a thermoventilated tank (ca. 10 m3 / 350 ft3) for continuous feeding to reactors: the tank capacity supplies fuel for an average of 25/50 hours (depending on biomass quality / power generated). A forced ventilation system blows hot air from the engines section to the tank, in order to reduce biomass moisture to a proper degree for gasification, which is around 10/12%. This feature allows to introduce also a high moisture content woodchips (up to 35%), once the CHP is running and generating heat.
The syngas is generated through multiple pyro-gasification reactors, named SBR30, which is the result of several years of R&D efforts made by RESET’s engineering team: it is a downdraft fixed bed reactor, where geometries and processes have been designed in order to minimize tar and condensate production. The reactor is composed of:
- loading hopper + rotary valve
- pyro-gasification reactor
- cyclone dust collector
- automated biochar collector
A single SBR30 is capable of generating ca. 35 kWe of corresponding required gas volume: for this reason, every SYNGASMART® (except for the 30 kWe model) is equipped with 2 or 3 reactors, according to power. Beside this, the multiple reactors configuration allows separate maintenance activities: therefore, the plant can still run on one line while servicing the other one.
The generated syngas flows first through dust-removing cyclones, and then through the jacketed vessel (gasifier) in order to exchange heat and stabilize adequately the required reactions temperatures.
The biochar, a vegetable coal resulting after gasification, is removed through an automated augers system for subsequent storage and usage, according to the specific situation. It still has some energy content, in addition to the well known fertilizing properties.
The syngas at the cyclone exit has high temperatures (ca. 300 °C / 570 °F) and some impurities: therefore it needs to be cooled down and filtered before piping it off to the genset. For this reason, SYNGASMART® CHPs are equipped with a double stage conditioning system for each gas generation line (2 or 3). This system comprise:
- condensation and cooling unit (air/water heat exchanger) with thermal recovery, steam condensation and condensate collection buffer;
- double biomass ‘packed bed’ mechanic filter, where the surface of woodchips retain and absorb the last residual tar, still present in the gas flow; once the filter has exhausted its properties, it is put back into the loading tank in order to be gasified and generate additional syngas, and replaced with fresh woodchips. It is a closed, no-waste cycle.
SYNGASMART® CHPs generate energy through standard internal combustion engines, with proper adjustments to operate with a low energy gas, coupled with three-phase synchronous generators, thus forming a Genset. Both of them are chosen among the highest market standards such as GM, Iveco, Marelli, Sincro and so forth, allowing fast spare parts management. The genset is responsible for either electricity and heat generation: a standard SYNGASMART® CHP is equipped with a double genset, the reason being that:
- the low calorific value of wood syngas requires bigger volumes to be treated, compared to gases such as LNG or LPG;
- servicing 2 smaller engines is cheaper than a bigger one;
- with 2 gensets, the CHP can still run on 1 line while servicing the other one, or it can run 50% in case of a reduced energy need.
SYNGASMART® is engineered to harvest heat all over the process through specific heat exchangers, either for self consumption (for example biomass drying) and for final user availability: from syngas production to internal radiant heat, from engine’s coolant to flue gases. The most of heat is thus recovered and made available in form of hot water or steam.
It is also possible to turn heat into cooling through a chiller (absorption refrigerator that uses a heat source to provide the energy needed to drive the cooling process), useful for food storage, air conditioning and other purposes. This upgrade transforms cogeneration into TRIGENERATION.
SYNGASMART® CHPs are operated either on site and via internet through a specific software (SCADA) controlling either the automation electric panel and the power panel; each parameter is measured, controlled and recorded: biomass loading, gasifier’s pressures and temperatures with alert control, biochar collection augers, filter temperatures and pressures, blower, air/syngas mix, engine’s rpm, grid-tie control, electricity generation, thermal recovery, performance data recording and telemetry.