Accurate models and realistic simulations are essential in developing cleaner and more efficient coal- and biomass-fired boilers. Using the CFD simulation software Fluent The University of Iowa created a model of an industrial boiler that adequately compares the practice of co-firing biomass and coal against firing only coal. The simulations used in this comparison, show significant circulation zones and an unrealistic temperature profile inside the boiler heat exchanger region. This model is effective for comparing the relative decrease in emissions when co-firing with biomass versus exclusively coal combustion, but it does not present a realistic simulation of biomass or coal combustion. The purpose of the current work is to develop a more realistic baseline coal combustion model. Calculations for the proximate and ultimate analysis of coal, as well as properties necessary for energy and mass flux computations, have been updated in the current model. The fuel bed model - a simple two-dimensional distribution of energy and mass fluxes from the grate - was kept the same due to the complexities of fuel bed modeling. Simulation boundary conditions and flow models were tested and modified to determine the most realistic model settings. The geometry and mesh grid of the boiler model were also varied in an attempt to fix problematic areas. Several approaches were implemented in an effort to reduce the circulation zones and generate a realistic temperature profile. The negative energy source term in the boiler representing the energy removed by the water pipes in the heat exchanger was analyzed, and different configurations of this sink were tested. Finally, the heat exchanger models built in to Fluent were studied and implemented. These models proved to be the most effective in reducing recirculation zones and decreasing high temperature gradients. While the current model of the coal-fired boiler has a higher overall temperature than the previous one, circulation zones are almost completely eliminated, the flow path has been improved, and the temperature profile in the boiler is more realistic.

QC 20100601

Carryover particles are partially/completely burned black liquor particles entrained in the flue gas in kraft recovery boilers. Understanding how carryover particles form and deposit on heat transfer tube surfaces is critically important in the design and operation of a recovery boiler. The tendency for a carryover particle to deposit on a tube surface depends on the particle temperature and composition at the moment of impact. This study was the first to examine systematically how carryover particle composition changes with the black liquor chemistry and burning conditions. The effect of black liquor composition and particle size, gas composition (O2 and SO2 concentrations) and temperature on the composition of carryover particles were studied using an Entrained Flow Reactor (EFR). Field studies were conducted on three operating boilers, where an air-cooled probe was used to collect carryover samples at the superheater entrance. The results show that the chloride (Cl) and potassium (K) contents in carryover particles were linearly proportional to their contents in black liquor. Cl and K were depleted during black liquor combustion due mainly to the vaporization of NaCl and KCl. The depletion of Cl is about three times greater than that of K. The significant depletion of Cl implies that carryover particles contain much less Cl, and hence, are less sticky than previously expected from black liquor composition. A dynamic model was also developed to predict the composition of carryover particles as a function of black liquor composition and burning conditions. Based on the data obtained experimentally in this study, the kinetic equations for the oxidation of sulphide available in the literature were modified and incorporated into the model to improve its sulphide and sulphate predictions. The model predicts the main components of carryover particles formed in both the EFR and three operating recovery boilers reasonably well, except for the K content, which is slightly over-predicted at high O2 concentrations (or high particle temperatures). Based on the predicted composition, it is possible to determine the thermal properties of carryover and to assess its fouling propensity in the boiler. The information helps boiler manufacturers and operators to identify locations in the boiler where massive carryover deposition may occur and to devise appropriate control strategies to minimize fouling and to improve boiler thermal efficiency.

Carryover particles are partially/completely burned black liquor particles entrained in the flue gas in kraft recovery boilers. Understanding how carryover particles form and deposit on heat transfer tube surfaces is critically important in the design and operation of a recovery boiler. The tendency for a carryover particle to deposit on a tube surface depends on the particle temperature and composition at the moment of impact. This study was the first to examine systematically how carryover particle composition changes with the black liquor chemistry and burning conditions. The effect of black liquor composition and particle size, gas composition (O2 and SO2 concentrations) and temperature on the composition of carryover particles were studied using an Entrained Flow Reactor (EFR). Field studies were conducted on three operating boilers, where an air-cooled probe was used to collect carryover samples at the superheater entrance. The results show that the chloride (Cl) and potassium (K) contents in carryover particles were linearly proportional to their contents in black liquor. Cl and K were depleted during black liquor combustion due mainly to the vaporization of NaCl and KCl. The depletion of Cl is about three times greater than that of K. The significant depletion of Cl implies that carryover particles contain much less Cl, and hence, are less sticky than previously expected from black liquor composition. A dynamic model was also developed to predict the composition of carryover particles as a function of black liquor composition and burning conditions. Based on the data obtained experimentally in this study, the kinetic equations for the oxidation of sulphide available in the literature were modified and incorporated into the model to improve its sulphide and sulphate predictions. The model predicts the main components of carryover particles formed in both the EFR and three operating recovery boilers reasonably well, except for the K content, which is slightly over-predicted at high O2 concentrations (or high particle temperatures). Based on the predicted composition, it is possible to determine the thermal properties of carryover and to assess its fouling propensity in the boiler. The information helps boiler manufacturers and operators to identify locations in the boiler where massive carryover deposition may occur and to devise appropriate control strategies to minimize fouling and to improve boiler thermal efficiency.

A modified furnace, which burns diesel oil is adopted to study the combustion characteristics and the pollution of the exhausting products under certain designing and operating conditions. The different equivalence ratios and swirl numbers can be obtained by adjusting the flow rate of both axial air and tangential air. The controlling ranges of the various experimental parameters include the equivalence ratios from 0.8 to 1.1, the jet oil pressures from 7 kg/cm² to 9 kg/cm², the open angles of the plate 0¢X and 45¢X, the swirl numbers from 0 to 1.0, the flow rates of the recirculated flue gas from 0% to 12%. The effects of the controlling variables on the combustion characteristics and the formations of pollutants within combustion chamber are studied in this reseach. A photographic technology is used to study the flame structures for helping us to understand the behaviors of the flame under various operating conditions. Under the equivalence ratios from 0.8 to1.1, the concentrations of the average NO and CO decrease, at the lower equivalence ratio. However, the concentrations of the average NO and temperature increases monotonously when jet oil pressure increases. The plate open angle 45¢X is useful for the mixing of both fuel and air, so that the open angle of the plate have important effects on both the temperature of combusion gas and the formation of pollutant NO. When the plate open angle 45¢X and the swirl number is 0.6, the flow rate of NO in the exhaust duct is the lowest. At equivalence ratio 0.8, the average NO concentration in exhaust duct decrease, when the flow rate of the recirculated flue gas increase. Our experiments display that the optimized operating condition is at the plate open angle 45¢X, the swirl number 1.0 and the recirculation rate of the flue gas 12%. NO can be reduced to 32% in this condition, and heat efficiency is reduced only about 3.7%, so we can achieve the request of reducing efficiency to much, the formation of pollutant without influencing the combustion. Under the condition of swirl number 0 and the open angle of the plate at 0¢X and 45¢X the color of the flame in the primary combustion region are white-yellow. In the other hand, at the swirl number 1.0, the color of the flame out of the primary combustion region at the swirl number 1.0 exhibits the red color due to the formation of CO2 and water vapor. The red color region at the swirl number 1.0 is much larger than that at the swirl number 0.

Abstract The special internet organization of small and medium enterprise administrations in Taiwan is famous in this world. Interaction in each other is the main factor to conduct such a relationship. From observing the boss of small enterprise administrations, we saw that when small and medium enterprise administrations in Taiwan face inconstant environment, they set up internet organization for survival. The agility and flexibility they showed have competition advantage against big business. At present, various work fields get their necessary materials by authorizing others and it became the main flow for development. In such tendency, for these enterprise administrations, how to built good interaction with authorized factories and create better competition advantage are problems they think about. Most inland boiler business existed as small enterprise administrations. The development of their relationship from how knowing each other till broken relationship, all cooperative conditions included in such relationship are the topic in this study. This study chose 5 bosses working in boiler for more than 15 years as our interviewers. The topic was interaction between boiler business and authorized factories. We processed deep interview to these interviewers by structural outline. We discussed the results by dividing the content of interview into four steps. The symptoms and problems at every step were analyzed since they are knowing each other, cooperation, maintaining relationship till breaking relationship. 1. Knowing each other: when they didn't know each other, they would give the first trust to subjects by vectors, such as friendship, consanguinity, etc. 2.Cooperation: according the interview results, the cooperative styles are divided into three parts, (1) market style, (2) team style, (3) project united style. 3. Maintaining and development: maintaining relationship was across social activities. Utilizing general activities could get rest time and improve relationship. 4.Breaking: trust was the first for cooperation. When doubting or finding subjects not following rules or invading private benefit, trust danger appeared because of broken benefit cooperation. It was the main factor causing such broken relationship.

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Pulp and paper mills are high power consuming industries. Pulp and integrated mills produce power via steam turbines in recovery boilers. Due to high power prices and the fact that biomass combusted in the recovery boiler is considered as green energy, there is today a desire to always increase the power generation when investing in new recovery boilers. In order to increase power output from the steam turbine the steam data (i.e temperature and pressure) needs to be increased. With higher steam temperature follows a higher risk of corrosion due to the non process element potassium in the boiler fuel. The uncertainties of high temperature corrosion and the unpredictable environment in the furnace makes it difficult to design recovery boilers. This results in higher investment cost and could lead to less profit for the mill buying the boiler. The question then stands whether the revenue obtained from the higher power generation, is higher than the investment made for the upgrade in order to produce the higher steam data over a certain time. And more specifically what steam data will be the most economical, when comparing revenue from power generation with investment cost? In this study, together with ÅF Industry AB, four boilers with different steam data (Boiler A: 38.5 bar, 450°C; Boiler B: 92 bar, 480°C; Boiler C: 106 bar, 500°C; Boiler D: 115 bar, 515°C) were compared. The boilers were compared for four potassium levels: 1.0wt%, 1.5wt%, 2.5wt%, 3.5wt%. And two values of power were used, 300 SEK/MWh and 700 SEK/MWh. The marginal differences between the boilers were: the amount of material used in the superheaters in order to produce different steam data; the type of material used in the superheaters and the furnace; whether an ash-treatment system was needed (in order to purge potassium from the process); the turbines and generators; whether a feed water demineralization equipment was needed; the yearly cost for make-up chemicals (due to usage of an ash-treatment system) and the amount of power generated. The boilers investment cost and net yearly revenue were compared in order to determine the marginal pay-off in years. The most economical choice of boiler for the different potassium levels for 300 SEK/MWh: 1.0wt%, Boiler D; 1.5wt%, Boiler C; 2.5wt%, Boiler B; 3.5wt%, Boiler D (A). And for 700 SEK/MWh: 1.0wt%, Boiler D; 1.5wt%, Boiler C; 2.5wt%, Boiler D (B); 3.5wt%, Boiler D. The conclusion in this thesis was that the deciding factor is whether the boiler is in need of an ash-treatment system. Higher steam data is preferable as long as ash-treatment can be avoided. However, when comparing two boilers with ash-treatment the one with higher steam data is more feasible. Low steam data, such as boiler A, will never be feasible, regardless of potassium level and value of power.