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MEASUR-Tools-Suite v1.0.11
The MEASUR Tools Suite is a collection of industrial efficiency calculations written in C++ and with bindings for compilation to WebAssembly.
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This calculator estimates the benefit of using waste heat from a high-temperature process to supply heat to a low-temperature process. The calculation uses flue gas properties, process firing rates, exhaust temperatures, available heat, and fuel cost. The method is based on standard industrial practice for process heat recovery.
The calculation follows a top-down approach:
Relevant formulas and symbol definitions are documented below.
Total energy savings from cascading heat.
The total energy savings is calculated by multiplying the hourly energy savings by the effective operating hours.
\begin{equation}\label{eq:cascade-high-to-low-total-energy-savings} E_{savings} = E_{hourly} \cdot H_{eff}\end{equation}
| \(E_{savings}\) | Total energy savings \([\unit{ \MMBtu\per\year}]\) |
| \(E_{hourly}\) | Hourly energy savings \([\unit{ \MMBtu\per\hour}]\) |
| \(H_{eff}\) | Effective operating hours \([\unit{ \hour\per\year}]\) |
Hourly energy savings from cascading heat.
The hourly energy savings is the minimum of the equivalent energy supply and the low-temperature process firing rate.
\begin{equation}\label{eq:cascade-high-to-low-hourly-energy-savings} E_{hourly} = \min(E_{supply}, F_{low})\end{equation}
| \(E_{hourly}\) | Hourly energy savings \([\unit{ \MMBtu\per\hour}]\) |
| \(E_{supply}\) | Equivalent energy supply \([\unit{ \MMBtu\per\hour}]\) |
| \(F_{low}\) | Low-temperature process firing rate \([\unit{ \MMBtu\per\hour}]\) |
Equivalent energy supply to the low-temperature process.
The equivalent energy supply is calculated by dividing the heat exchanger energy rate by the available heat of the low-temperature process.
\begin{equation}\label{eq:cascade-high-to-low-eq-energy-supply} E_{supply} = \frac{Q_{hx}}{AH_{low}}\end{equation}
| \(E_{supply}\) | Equivalent energy supply \([\unit{ \MMBtu\per\hour}]\) |
| \(Q_{hx}\) | Heat exchanger energy rate \([\unit{ \MMBtu\per\hour}]\) |
| \(AH_{low}\) | Available heat of low-temp process \([\unit{ \unitless}]\) |
Energy transfer rate through the heat exchanger.
The heat exchanger energy rate is calculated by multiplying the flue gas volume, specific heat, density, and temperature difference, then dividing by the conversion factor.
\begin{equation}\label{eq:cascade-high-to-low-hx-energy-rate} Q_{hx} = \frac{V_{flue} \cdot C_{p} \cdot \rho_{flue} \cdot \Delta T}{CF}\end{equation}
| \(Q_{hx}\) | Heat exchanger energy rate \([\unit{ \MMBtu\per\hour}]\) |
| \(V_{flue}\) | Flue gas volume \([\unit{ \scf\per\hour}]\) |
| \(C_{p}\) | Specific heat of flue gas \([\unit{ \btu\per\pound\degreeFahrenheit}]\) |
| \(\rho_{flue}\) | Flue gas density \([\unit{ \pound\per\scf}]\) |
| \(\Delta T\) | Temperature difference \([\unit{ \degreeFahrenheit}]\) |
| \(CF\) | Conversion factor (e.g., 1,000,000 for MMBtu) \([\unit{ \unitless}]\) |
Flue gas volume from the high-temperature process.
The flue gas volume is calculated using the firing rate, stoichiometric air volume, excess air, and fuel heating value.
\begin{equation}\label{eq:cascade-high-to-low-flue-volume} V_{flue} = \frac{F_{high} \cdot SAV_{high} \cdot (1 + EA_{high}) \cdot CF}{HV_{fuel}} + \frac{F_{high} \cdot CF}{HV_{fuel}}\end{equation}
| \(V_{flue}\) | Flue gas volume \([\unit{ \scf\per\hour}]\) |
| \(F_{high}\) | High-temperature process firing rate \([\unit{ \MMBtu\per\hour}]\) |
| \(SAV_{high}\) | Stoichiometric air volume \([\unit{ \scf\per\MMBtu}]\) |
| \(EA_{high}\) | Excess air (fraction) \([\unit{ \unitless}]\) |
| \(CF\) | Conversion factor (e.g., 1,000,000 for MMBtu) \([\unit{ \unitless}]\) |
| \(HV_{fuel}\) | Fuel heating value \([\unit{ \btu\per\scf}]\) |
Flue gas properties for both processes.
Flue gas properties such as stoichiometric air volume, excess air, available heat, specific heat, and density are calculated for both the high-temperature and low-temperature processes using standard methods.
Modules | |
| Total Energy Savings Formula | |
| Total energy savings from cascading heat. | |
| Hourly Energy Savings Formula | |
| Hourly energy savings from cascading heat. | |
| Equivalent Energy Supply Formula | |
| Equivalent energy supply to the low-temperature process. | |
| Heat Exchanger Energy Rate Formula | |
| Energy transfer rate through the heat exchanger. | |
| Primary Flue Gas Volume Formula | |
| Flue gas volume from the high-temperature process. | |
| Flue Gas Properties | |
| Flue gas properties for both processes. | |
Files | |
| file | cascade_heat_high_to_low.h |
| Functions to calculate energy savings from using exhaust gas (waste) of high temperature to supply heat to low temperature equipment. | |
Namespaces | |
| namespace | cascade_heat_high_to_low |
| Cascade heat recovery calculations for process heating systems. | |
Classes | |
| struct | cascade_heat_high_to_low::CascadeHeatHighToLowResults |
| Results of the cascade heat high-to-low calculation. More... | |
Functions | |
| CascadeHeatHighToLowResults | cascade_heat_high_to_low::calculateCascadeHeatHighToLow (const gas_composition::GasComposition &gas_compositions, double fuel_hv, double fuel_cost, double pri_firing_rate, double pri_exhaust_temp, double pri_exhaust_o2, double pri_comb_air_temp, double pri_op_hours, double sec_firing_rate, double sec_exhaust_temp, double sec_exhaust_o2, double sec_comb_air_temp, double sec_op_hours, double fuel_temp_f=60, double ambient_air_temp_f=60, double comb_air_moisture_perc=0) |
| Calculates the energy and cost savings from cascading heat from a high-temperature to a low-temperature process. | |
| CascadeHeatHighToLowResults cascade_heat_high_to_low::calculateCascadeHeatHighToLow | ( | const gas_composition::GasComposition & | gas_compositions, |
| double | fuel_hv, | ||
| double | fuel_cost, | ||
| double | pri_firing_rate, | ||
| double | pri_exhaust_temp, | ||
| double | pri_exhaust_o2, | ||
| double | pri_comb_air_temp, | ||
| double | pri_op_hours, | ||
| double | sec_firing_rate, | ||
| double | sec_exhaust_temp, | ||
| double | sec_exhaust_o2, | ||
| double | sec_comb_air_temp, | ||
| double | sec_op_hours, | ||
| double | fuel_temp_f = 60, |
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| double | ambient_air_temp_f = 60, |
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| double | comb_air_moisture_perc = 0 |
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| ) |
Uses flue gas properties and process parameters to estimate the benefit of using waste heat from a primary (high-temp) process to supply heat to a secondary (low-temp) process.
| [in] | gas_compositions | Fuel gas composition for flue gas calculations. |
| [in] | fuel_hv | Fuel heating value \([\unit{Btu/SCF}]\) |
| [in] | fuel_cost | Fuel cost \([\unit{USD/MMBtu}]\) |
| [in] | pri_firing_rate | Primary process firing rate \([\unit{MMBtu/hr}]\) |
| [in] | pri_exhaust_temp | Primary process exhaust temperature \([\unit{\degreeFahrenheit}]\) |
| [in] | pri_exhaust_o2 | Primary process exhaust O2 (fraction) |
| [in] | pri_comb_air_temp | Primary process combustion air temperature \([\unit{\degreeFahrenheit}]\) |
| [in] | pri_op_hours | Primary process operating hours \([\unit{hr/yr}]\) |
| [in] | sec_firing_rate | Secondary process firing rate \([\unit{MMBtu/hr}]\) |
| [in] | sec_exhaust_temp | Secondary process exhaust temperature \([\unit{\degreeFahrenheit}]\) |
| [in] | sec_exhaust_o2 | Secondary process exhaust O2 (fraction) |
| [in] | sec_comb_air_temp | Secondary process combustion air temperature \([\unit{\degreeFahrenheit}]\) |
| [in] | sec_op_hours | Secondary process operating hours \([\unit{hr/yr}]\) |
| [in] | fuel_temp_f | Fuel temperature \([\unit{\degreeFahrenheit}]\) (default: 60) |
| [in] | ambient_air_temp_f | Ambient air temperature \([\unit{\degreeFahrenheit}]\) (default: 60) |
| [in] | comb_air_moisture_perc | Combustion air moisture percent (default: 0) |
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