| OCR Text |
Show simulate the stoker grate pressure drop. Partition plates were used to divide the inlet plenum into sections, each with an adjusta~le damper inlet similar to that of the prototype umt. The OFA jet configuration was enlarged an appropriate in the isotnermal model to accurately simulate the mixing between these jets and the simulated hot main stream flow in the modeL Thus both the 1et to main stream mass flow and momentum ratlos could be maintained in the model and the prototype. Typical OFA designs that were modeled included: 1) Two levels of OFA nozzles, 2) Three levels of OF A nozzles, 3) Front and rear wall OFA nozzles. The model testing included flow visualization, three dimensional mapping, and tracer gas m1x1n.g tests. For. the mixing tests, tracer gas was dlrected to varIous inlet sections under tlle s1mulated stoker grates Ftg. 7 - Isothermal Chemical Recovery Bol1er Flow Model 123 MODELING CASE STUDIES In this section we w1ll review some of the results from the isothermal modeling tests carried out in the previously described. moaels. BURNER STUDIES - Under the experimental test program for the development of a high-turndown burner (6), two approaches were used" to evaluate the aerodynamics of the d1fferent burner des1gns under appropriate isothermal flow conditions. The first produced Qual1tat1ve data by flow visual1zation utiliz1ng neutrally buoyant hel1um bubbles, yarn streamers, high resolution black and white photography, and a videotape recording system. Figure 5 showed the use of the hel1um bubble technique. The secon~ approach produced Quantitative three d1menslOnal velocity and pressure mapping data, based on the use of a five hole pitot tube with automati~ travers1ng and data acquisition. The combmatlon of data obtained from the flow visuallzation and the three dimensiona1 ve1oc1ty and pressure measurements was utt1ized to tnterperet the near field aerodynamics of the different burners. As described by Marion and Towle (6), the aerodynamic features of the alternate designs were compared against those from otfler investigators studies ( for example, see Hagiwara and Bortz (23) to aid flame attachement and stability. Figure 8 gives a typical result from the flow v1sual1zatfon tests- in this case the resuJts are for a' swirl concept burner. For th1s case the sw1rl level was low, however there ~s cons1derable mixing, indicated by the rapId outward dispersion of the bubble strear:ns, but there is no recirculation zone, thus thIS case would not be good from a flame stabtHzatton standpOint. An example of the velocity vector data is shown In Figure 9, representing a swirl concept burner, but with a hfgher degree of swirl than the prevtous case. The data shown represents a centerllne vertical slice through the burner model and Is simt1ar to the flow visual1zation model shown in the previous figure. These resuJts Ind1cate a zone of recirculating flow. Based on the analysis of the data taken from these tests, a swirl type deSign, Concept B, was chosen for combustion testfng. This des1gn provided good mixing and turbulent intenSity a wide strong recirculation zone, and acceptable pressure losses. As a result of a series of combust10n tests in a fu11-scale burner facUlty, this design was shown to have the best combustion properties and fully met the program goals. That ls, during combustion testing it proved to have improved flame. attachment properties as compared to the prevlous standard design, which led to better turndown and low excess air performance. |
