Ximilo dynamic composting process simulator - P&IP BV

Usually, composting of organic matter is a batch process where a static pile of organic matter is areated. The objective of composting is stabilization and/or mass reduction. These are accomplished by aerobic microbial conversion of substrate into cell material and heat, where the heat evolved heat warms up the composting material, the air and vaporizes free water.

In many cases, composting is an industrial process with high throughputs, extended installations and appreciable added value.

Difficulties in understanding the composting process arise from simultaneous proceeding phenomena along the air flow path through the pile:
changing solids and air conditions
concurrent hydrolysis and microbial growth, decay and conversion
heat and mass exchange between solids and air
Since the composting process is a static matrix batch process, it is characterized by spatial and memory effects which make it complex to understand, not to say optimize.

The composting process is controlled (manipulated) by:
the initial compostion of the batch (feedstocks, recycle compost, bulking agent)
air quantity (flow) and quality (temperature, oxygen content, relative humidity) during the batch
duration of the batch
(assumption: intial permeability and porosity are homogeneous)

Because only few and simple meausurements are available and the batch duration is 1 - 3 weeks, learning from practice and optimization is limited and very laborious .

In conjunction with the Ximilo® composting simulator one can compare simulation results with measurements and tune parameters in the model. When the model is sufficient similar to the real composting process, one can suggest and test alternative control strategies. Many more process variables can be followed and evaluated: insight in the process increases significantly.

The Ximilo® dynamic composting simulator is a versatile simulator of the composting process in a tunnel. It is adaptable by the user for virtually all feedstocks, tunnel dimensions, equipment sizes, control configuration and control strategies.
If not tuned to a specific process, it is not a predictive simulator. However parametrization with theoretical values should be a good starting point.

In the model, the composting pile is divided in 8 horizontal layers, to account for the spatial effects. Each layer is handled as a control volume for the solids and a control volume for the air. The model of the processes in the solids comprises:
microbial growth and conversion (linked together by the Yield factor)
the growth model is Contois (which can be parametrized as Monod)
hydrolysis of solid substrate
decay of active microbes
conversion is according the chemical reaction, where water is formed as a liquid and the corresponding superior heat is liberated
a simplified model for nitrogen is included: Kjeldahl-N in excess for growth is converted as aqueous ammonia, which is in equilibrium with the ammonia in the air at the actual temperature
the heat of conversion is accumulated in the solids
physical transport equations determine the heat and mass exchange with the passing air
the solids water activity curve (sorption isotherm) determines the water exchange at higher dry matter values
Microbial and hydrolysis reaction rates depend on various conditions (temperature, oxygen content etc). In the simulator, these are parametrizable curves. The multiplicative model approach is applied where more than one condition plays a role.
The tunnel plenum is a seperate control volume.

This dynamic simulator can be applied to optimize production by:
knowledge generation of specific composting processes and subsequent analysis of improvenment suggestions
instruction of operators


Please inquire for a full description of the simulator and feel free to check the opportunity for a demonstration.
Pricing on demand.
The composting simulator can also be employed by P&IP on a project basis in an optimization study.



Screens of Ximilo® Dynamic Composting Simulator


1 main operation screen: on the left hand side the Ximilo simulator dash is situated and is always visible; the first tab is the operating interface and also depicts all batch accumulative data




2 trend tab, is a standard Ximilo provision
Two trends with a maximum of 8 tags each can be visualized. Other trend configurations can be saved and loaded during run time.




3 Profile tab: presentation of the layers condition
This gives a dynamic view on the gradient of various key layer conditions.




4 Log tab, is a standard Ximilo provision
This defines the tags to be logged for application in trends or Excel.



An Excel application goes with the software to configure Excel graphs easily from any Ximilo datafile. For example:


5 Inspect tab, is a standard Ximilo provision to inspect and follow the actual value of selected variables.




6 Scenario tab, is a standard Ximilo provision
This allows the user to set up a standard sequence control of simulation runs.
Breakpoint simulation (not visulalized here) comprizes a maximum of three free configurable conditions (Condition1 AND/OR (Condition2 AND/OR Condition3)) at which the simulator stops if the overall condition is true.




7 Settings tab: the batch initial mixture and physical properties are entered; also the ambient air conditions
The composition of the initial tunnel inventory is defined, including some physical parameters of the batch (bulk density, initial temperature, flow conductance, mechanical strenght etc.). From these basic parameters a series of derived vaues are computed.
The intake air conditions are to be parameterized as a boundary condition (if not constant). Intake air is fresh ambient air, or reused air (from another tunnel, waste air etc.).




8 feedstock tab, this is a set of four feedstocks, and optionally a bulking agent and an active biomass, where the batch can be prepared of (tab settings)




9 kinetics tab: all rate determining parameters are entered here, included curved dependencies and the sorption isotherm of the composted material.




10 equipment tab: all composting "hardware" is defined here (tunnel dimensions, aereation floor properties, louvre dampers, fan curve and efficiencies, controller setings, controller setpoint trajectories etc.




11 simulator tab, this is a standard Ximilo page
Some basic simulator parameters are set here.
A login feature for technologists enables process and equipment configuration to be changed.