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Plant monitoring is the detailed evaluation of the performance of overall plants as well as of single plant components. In biomass combustion, gasification and pyrolysis plants as well as in biomass CHP plants and biorefineries monitoring represents an important basis for process optimisation, especially during the start-up phase and the first year of operation but also as a basis for trouble shooting.
The main objectives of the work regarding monitoring and optimisation of plants are the following:
- Plausibility check of the plant internal measurement and analyses devices
(e.g.: gas temperature measurements, heat and electricity measurements, gas analysers),
- Determination of the efficiencies of emission reduction measures
(dust separation efficiencies of cyclones, ESPs and baghouse filters; efficiencies of primary and secondary measures for NOx, SOx and HCl emission reduction respectively for the reduction of tar and soot in product or pyrolysis gases)
- Performance of detailed mass and energy balance calculations over single plant components as well as over the whole plant in order to determine their efficiencies or performance indicators
- Targeted optimisation of plant settings
- Identification of bottlenecks and malfunctions e.g. increased leakage flows, increased deposit formation on the reactor walls and in heat exchangers
- Detailed evaluation of the plant performance in order to optimise the plant settings with the aim to achieve operation at high efficiencies and low auxiliary energy consumption as well as regarding improved gas quality of product or pyrolysis gases.
Based on these evaluations suggestions for improvements are worked out and forwarded to the plant operator or plant manufacturer to discuss their implementation.
At BIOS plant monitoring is generally based on three different approaches:
- Long term monitoring of biomass conversion reactors, biomass CHP plants and biorefineries
- Dedicated test runs with accompanying plant monitoring at biomass conversion plants, biomass CHP plants and biorefineries
- CFD-aided simulation of biomass conversion reactors based on the data gained from test runs as well as mass and energy balancing over the plant for a targeted weak point analysis
Long term monitoring
The respective plant operation data needed for the monitoring are stored by the plants process control system over a certain period (some days or weeks) and then forwarded to BIOS, where they are evaluated by using special in-house developed data evaluation programs.
Link to Software Development
Dedicated test runs with accompanying plant monitoring
Within dedicated test runs which usually last for several days, plant operation data are collected by the process control system and additionally, samples from all relevant in-going and out-going streams are taken. Moreover, relevant parameters are determined by BIOS engineers separately with mobile measurement and analysis devises. Examples are:
- Gas composition
- Temperatures and volume flows of the gas in different plant sections
- Reactor temperatures
- Deposit formation in conversion reactors and heat exchangers (applying deposit probes)
- Particle size distribution and concentration of fly ashes and aerosols (fine particulates) in different sections of the plant
- Fuel and ash sampling and subsequent chemical analyses of the samples taken
- Tar measurements and analyses of product or pyrolysis gases
- Detailed analyses of the gas produced
Based on these measurement and analyses data as well as on mass and element balances calculated over single plant components respectively the whole plant, the plant performance is evaluated.
CFD-aided simulation of biomass conversion reactors
CFD simulations allow for the spatially resolved calculation and visualisation of the turbulent reacting flow in biomass conversion reactors. An improved understanding of the fundamental physical and chemical processes as well as of the distributions of temperatures, flows and concentrations of gas phase compounds can thereby be gained.
CFD-aided plant monitoring of plants is of great advantage, since it is based on real operation data and therefore allows for a detailed weak point and error analysis. As an example, hot-spots causing slagging as well as reasons for too high contaminant emissions like a poorly mixed gas or too short residence times at sufficiently high reaction temperatures can be identified. Consequently, CFD-aided monitoring provides for an efficient evaluation and optimisation of plant operation.
Link to CFD Simulations
Aims of CFD-aided plant monitoring:
- Validation of models / check of simulation results from preceding design studies
- Determination of the effective heat transfer coefficient of refractory linings under consideration of ash deposit layers on reactor walls
- Calibration of thermocouples by means of combined suction pyrometer measurements / CFD simulations as a basis for an improved temperature control in the conversion reactor
- CFD analysis of plant operation as a basis for an improved control concept and an optimisation of operation
- Error and weak point analysis of conversion reactors and their geometry as a basis for retrofitting measures
The following improvements concerning plant operation can be achieved with these measures:
- Reduction of CO and NOx emissions – identification of strain formation and weakly stirred gas flows
- Reduction of too high tar or soot concentrations in the product or pyrolysis gas – identification of strain formation and weakly stirred gas flows
- Compliance with the target air ratios
- Reduction of hard ash deposit formation – identification and avoidance of local temperature peaks
- Reduction of erosion and material stress – identification and avoidance of velocity and temperature peaks
- High plant availabilities