Heat balances pyrolysis reactors

In the second example, that of an industrial pyrolysis reactor, simplified material and energy balances were used to analyze the performance of the process. In this example, linear and nonlinear reconciliation techniques were used. A strategy for joint parameter estimation and data reconciliation was implemented for the evaluation of the overall heat transfer coefficient. The usefulness of sequential processing of the information for identifying inconsistencies in the operation of the furnace was further demonstrated. 

The major terms in the heat balance of a pyrolysis reactor are ... 

A chrome -alumel thermocouple was set in close proximity to the sample inside a reactor. The reactor was made of a quartz tube which was surrounded by a tubular furnace. In a typical coal pyrolysis run, the coal sample (20-30 mg) was placed in a platinum boat which was suspended from the quartz beam of the TGA balance. The coal particle size used was 100-200 mesh. Samples were heated to desired temperatures at linear heating rates or heated iso-thermally under various gaseous environments. 

The throughput of the plant is definitely limited by the capacity of heat radiation of the commercial fire tubes. The prototype reactor allowed a space-time yield of 1.3 t/m fluid bed per hour. The heating value of the pyrolysis gas produced was sufficient to balance the heat demand of the process. 

The pyrolysis experiments were conducted in an electrically heated, once-through tubular flow reactor, designed to simulate the time-temperature history experienced in commercial steam-cracking operations. Reactor effluent compositions were ascertained by gas chromatograph and mass spectrometer analyses. Material and hydrogen balances could always be effected, with typical closures of 98 2 wt %. 

A wood cylinder is vertically positioned in the uniformly heated zone of the reactor, through a suspension system, which is connected to a precision balance. The sample is exposed to the same radiative heat flux along the lateral surface. For each chosen radiation intensity, steady temperatures of the radiant heater are achieved within a couple of minutes (maximum heating rates of about 750K/s) but, given the thick sample, pyrolysis takes place under heat transfer control. 

A vortex tube has certain advantages as a chemical reactor, especially if the reactions are endothermic, the reaction pathways are temperature dependent, and the products are temperature sensitive. With low temperature differences, the vortex reactor can transmit enormous heat fluxes to a process stream containing entrained solids. This reactor is ideally suited for the production of pyrolysis oils from biomass at low pressures and residence times to produce about 10 wt % char, 13% water, 7% gas, and 70% oxygenated primary oil vapors based on mass balances. This product distribution was verified by carbon, hydrogen, and oxygen elemental balances. The oil production appears to form by fragmenting all of the major constituents of the biomass. 

Data has been presented which suggests that moisture can enhance the production of tar from the pyrolysis of large wood particles using conditions that occur in a large scale reactor where the heat flux a particle experiences is quite constant. The most favorable conditions result in about 70% of the reacted biomass becoming tar. If one assumes that the mass balance discrepancy results from tar condensing on reactor surfaces, this is a conservative estimate. 

The continuous fast pyrolysis of wood sawdust has been studied in a Lapple type (2.8 x 10" m diameter) cyclone reactor heated between 893 and 1330 K ( ). The wood particles carried away by a flow of steam enter tangentially into the cyclone on the inner hot walls of which they move and undergo decomposition. Mass balances show in all the cases, a very low fraction of char (< 4 %) while the gasification... 

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