Capítulo 2. La Educación Patrimonial y las Tecnologías de la Información, la
2.4. Criterios, enfoques y modelos de educación patrimonial
The quantity of liquid residues produced from each run was collected and measured. Samples of the condensate were collected in sample bottles and analysed for (i) pH; ( ii) electrical conductivity ( iii) turbidity; and (iv) chemical oxygen demand (COD).
Chapter Five: The air gasification of wood}' biomass 165
5 . 3 . 7 SOLID RESIDUES SAMPLING
Solid residues were collected from the ash port, blast tube and cyclone (Figures 5 .4 and 5 . 6) and weighed. Fine char from the cyclone was used in liquid residues cleaning tests (see section 5.4.9).
5 . 3 . 8 THEORY, DEFINITIONS AND DERIVATIONS
The feed, water, air and product gas flows, and the quantities of solid and liquid residues collected at the end of each run were multiplied by the period of run (minutes) to obtain the total quantity of each component in the system. These data were used to derive the material flows (as inputs and outputs) of the gasifier. Material flows were converted to weight over time to provide genuine comparisons between feedstocks, and between runs. The quantity of water in the feedstock and after release, flowing through the system, (g/h) was calculated from moisture content measurements, weight of batch feed loaded into the gasifier, and the time taken to exhaust the charge. Run averages of the input and output flows data were used to calculate the mass balance, residence time, ga<;ification and specific gasification rates, hearth load, equivalence ratio (ER), and the net water formation. Gas composition was used to calculate the gas relative density, heating value and other quality and conversion efficiency measures.
• Mass balances
There were 2 inputs into the system - feedstock and air with masses MF and MA• The third input - water depended on the moisture content of the feedstock, and could be presented as Mw. The output
stream<; from the reactor were product gas (MPG), solid residues (MSR), and liquid residues (MLR). From the law of conservation of mass, the mass balance was derived as:
The main interest was product gas, while solid and liquid residues were only monitored for determining overall conversion efficiencies, and for their disposal requirements.
• Residence time (s)
Residence time was calculated as the ratio of air velocity (Va, mls) into the gasifier, to the fire-bed length (1; 0.275 m), ignoring the presence of the fuel. It is the time the gas produced remains within the gasifier fire-bed region:
Chapter Five: The air gasification of wood.>, biomass
• Specific dry gasification rates (SGR)
166
The average rate of dry fuel gasification (g/s) per unit gasifier grate area (0.01 23 m2) was
determined from mass flows. and the moisture contents of the fuel determined on batch loading. The specific gasification rate was given as:
SGR = (dry rate of fuel use, g/s)/O.0 1 23 m2
• Hearth load (Superficial gas velocity) (Hd
The hearth load is given by the volumetric flow rate of the product gas (V, m3/s) divided by
the cross sectional area of the gasifier at the constriction (choke), (a, m2) . The hearth load defines the gas production rates expressed in gas volume per cross section area - time
(volume/area - time) = length/time = velocity:
• Equivalence ratio (ER)
H
LThe equivalence ratio (ER) defines the ratio of the mass of the oxidant (MA) to the mass of fuel
(MF) divided by the oxidant stoichiometrically required per unit mass of dry feedstock (6.2 1
kg/kg of dry wood). It expresses the quantity of air (MA) used as a proportion of the
stoichiometric air requirements (As) used to gasify a given unit of fuel :
• Net water formation (NWF)
NWF was calculated as the ratio of the difference between all water contained in the products
(including collected liquid residues and the gas moisture. MLR), to all the water in the feed
(Mw) for a given weight of the dry feedstock (MF):
• Product gas heating value
NWF = MLR - Mw / MF
Gas heating value was estimated as the sum of the calorific values of the components, each multiplied by the corresponding mole fraction, the sum so obtained being corrected for the
compressibility of the mixture (DIN 5 1 858, 1 982; Rose and Cooper, 1 977). The compressibility
or real gas factor was derived from an analogous sum of component contributions plus a sum of terms for the interaction between components.
The uncorrected sum of heating values of the combustible components (CV m:l may be derived as:
Chapter Five: The air gasification of woody biomass 167
where CV m was the summation of heating values of the product gas constituents (kJ/mol); Xf, X2, ....
are mole fractions, and CV" CV2, ... are heating values" (kJ/mol) of the product gas components.
The compressibility factor 2m for the mixture was given by:
where xH was the molecular fraction of hydrogen present in the mixture, and b], b2 '" are gas law
deviations of the components (except hydrogen), as defined by the ideal gas function:
where P ::: pressure. V = volume, R ::: the molar ideal (universal) gas constant, and T ::: the
thermodynamic ('absolute') temperature (0 K) (DIN 51858). The corrected calorific value (CV) of the gas was therefore given by:
CV = CVrrlZn • Heat value of the stoichiometric gas air mixture
The heating value of the mixture was calculated from the respective heating values, the stoichiometric oxygen requirements, and the volume of each component in the mixture:
1 2.68*v
CO
+ 1 0.8*vH2
+ 35.9*\/CH4
H·
Ig ::: 1 v V+ 2.38*
CO
+ 2.38*He
+ 9.52CH4
where Hg is the heating value of the stoichiometric mixture of producer gas and air in MJ/m3; and
vI is the volume fraction of the respective gases before mixing with air (FAO, 1986). • Cold gas efficiencies (CGE)
CGE was defmed as the ratio of output product gas energy to the input feed energy. • Product gas relative standard density
The relative density was estimated from the densities of individual product gas components:
P (real )
d (real)
=i