FluoSolids~ Reactor Calcining of lime Mud for the Sugar Beet Industry

Transcription

1 FluoSolds~ Reactor Calcnng of lme Mud for the Sugar Beet ndustry By: Laura K. Bums Dorr-Olver nc. Oak Brook, llnos Lews W. Clark Dorr-Olver nc. Mlford, Connectcut Lme mud waste n sugar beet refneres s a growng problem whch can be elmnated usng a flud bed recovery process. Sugar beet processng plants are under ncreasng envronmental pressure to cease the accumulaton of ths lme mud waste ple and to desst from the dust cloud that the ple can emt. Generally speakng the tradtonal sugar ndustry shaft klns are unsatsfactory for lme mud recovery necesstatng other technology. The purpose of ths paper s to present schemes for reclamng ths ple as a salable byproduct or as a recyclable product. The essence of the scheme s the flud bed calcner where the lme mud can be regenerated to lme and carbon doxde gas. The calcner s a two-compartment vessel as shown n Fgure 1. The upper compartment contans a fludzed bed of lme pellets. The dry lme mud s blown nto ths fludzed bed where the mud wth auxlary fuel s calcned to lme. The feed has trace amounts of sodum that melts and causes the lme to form a pellet whch accumulates n sze to become part of the fludzed bed. As the fludzed bed grows from the pelletzaton process a porton s transferred to the lower compartment where the pellets are cooled by the upflowng ar to be used n the calcnng compartment. Ths preheated ar then represents a fuel economy. Dorr-Olver has nstallatons performng ths process n the paper ndustry where a lme mud from the Kraft paper process s regenerated to lme pellets for return to slakng. The lme mud of the sugar beet ndustry s remarkably smlar to the lme mud of the paper ndustry. Table 1 shows some analytcal data on sugar beet lme mud whch we wll share here. Also, Dorr-Olver has conducted plot tests on sugar beet lme mud whch PRESENTED AT AMERCAN SOCETY OF SUGAR BEET TECHNOLOGSTS, FEBRUARY,

2 demonstrated the pelletzaton process and confrmed good product slakng characterstcs. Slakng tests of the pelletzed lme product were conducted by measurng out 200 ml of water at 20 C nto whch 50 grams of lme pellets were strred untl there was no further temperature rse. As a gude our understandng s that a good and medum qualty lme wll have the slakng characterstcs stated n Table 1. Table 1 Sze Analyses of dry sugar beet lme mud as feed to a calcner 10% greater than 10 mcron 25% greater than 7 mcron 50% greater than 4.5 mcron 75% greater than 3.1 mcron 90% greater than 2.5 mcron Typcal chemcal analyss of sugar beet lme mud as a calcner feed Antcpated product analyses from the calcner 83% ca co3 1% Mg co 3 2.5% Ca (OH)2 6.2% hydrated H20 0.1% Na and K 4.1% Acd nsoluble nerts whch ncludes S02 1.3% as so4 1.8% Soluble n acd as Fe, A1 and Msc. 88.2% Ca 0 3.4% ca so4 8.4% nerts 0.01% MgO 537

3 SLAKNG CHARACTERSTCS TEMPERATURE RSE FROM 20 C Medum Good Pelletzed Qualty Qualty Lme from a Tme Lme Lme Fludzed Bed sec '34 C 1 mn 39 C 100 sec 41 oc 2 mn 44 C 160 sec 48 C 3 mn 50 C 4 mn 34 C 4rc 54 C 7 mn 42 C 65 C 58 C 9 mn 72 C 58 C 15 mn 50 C We were dsapponted that ths typcal chemcal analyses whch was developed from a grab sample from an exstng ple dd not show a carbon content or calorfc value. Our understandng s that 400 to 800 BTU/lb. of heat value may be avalable n the lme mud from resdual organcs. Ths heat value would be released n the calcner as a fuel economy. The lme pellets wth ther sphercal shape are excellent for pneumatc conveyng, bn storage and other materal handlng. The antcpated product analyses s somewhat hgh n nerts such that the product would not qualfy as a hgh calcum commercal grade quck lme but the product would be salable to certan markets. The pellets are certanly very reactve n slakng. Dorr-Olver has plot facltes n Golden, Colorado, where your sample of lme mud can be calcned. We would consder plot testng mandatory to ascertan the product qualty. 538

4 One recovery process for the lme mud s to use the calcnng scheme of the paper ndustry. The ntent would be that lme mud generated durng a campagn would be stockpled and calcned ndependent of the sug~ beet process producng a salable byproduct. Perhaps other stes can transport ther mud to the calcner. Here the calcner s coupled wth a flash dryng system to drve off surface mosture. The dry feed s then blown nto the calcner as shown n the Fgure 2 flowsheet. Ths s a flowsheet for a 100 TPD product whch s one of our operatng systems. Ether natural gas or ol may be used for the auxlary fuel. A conservatve estmate of fuel usage s 7.5 mllon BTU/Ton product. Ths number presumes no heat value s avalable from the feed. Power usage s antcpated to be 115 KW/Ton. An order-ofmagntude nstalled captal cost for ths faclty s $3,800,000. A second, and more nterestng, scheme for recoverng lme mud s usng the fluosolds calcner to generate a lme product for slakng and to use the calcner offgases wth ther C02 content n the carbonaton step. Here the calcnng system s szed for the plant producton. The lme mud flter produces a 50% solds cake whch s ndrectly dred to a powder capable of beng blown nto the calcner. The FluoSolds calcner s usually desgned for 20% excess ar whch produces a C02 content n the calcner exhaust gases of 22% (dry bass). However, ths C02 content can be enhanced by oxygen enrchment of the ar to the calcner to produce the 28% C02 whch s normally seen n carbonaton. There could be a control loop between C02 content and oxygen. The hot calcner exhaust gases go to a scrubber for fnal dust removal and for heatng water to be used n slakng. Ths conceptual scheme s shown n Fgure 4. There s a certan nevtablty that ndefnte accumulaton of sugar beet lme mud wll stop. Perhaps the tme s now for plannng the alternates.,- 539

5 - F\uoSoflds /Cakr.er Dry T.me M~d ~ r. -Fu~l (G2s O Ol) Coofng.Compa;lmenl Fgure 1 ~wo Compartment Lme Mud Calc~ner 540

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