{"id":587,"date":"2020-11-25T11:34:47","date_gmt":"2020-11-25T07:34:47","guid":{"rendered":"https:\/\/tiwater.info\/en\/?p=587"},"modified":"2022-09-02T16:42:28","modified_gmt":"2022-09-02T12:42:28","slug":"the-calculation-of-carbon-dioxide-concentration-in-steam-condensate","status":"publish","type":"post","link":"https:\/\/tiwater.info\/en\/the-calculation-of-carbon-dioxide-concentration-in-steam-condensate\/","title":{"rendered":"The calculation of carbon dioxide concentration in steam condensate"},"content":{"rendered":"

Ivan Tikhonov<\/p>\n

Steam condensate is corrosive due to the presence of carbon dioxide in it. As a rule, the concentration of carbon dioxide in the condensate is required to be less than 20 mg\/l.<\/p>\n

The concentration of carbon dioxide in the condensate can be easily determined by knowing the concentration of bicarbonate ion in the feed water and the share of decomposition of bicarbonate in the thermal deaerator and then in the steam boiler.<\/p>\n

Carbon dioxide in the condensate appears due to the fact that in a steam boiler, bicarbonates decompose to form hydrate and carbon dioxide. Carbon dioxide is carried away with steam and then passes into condensate.<\/p>\n

Thus, if we assume that all bicarbonate is decomposed in the boiler, the concentration of carbon dioxide in the steam will be equal to the concentration of bicarbonate in the feed water in mg-EQ\/l.<\/p>\n

However, the bicarbonate in the boiler does not decompose completely. It is assumed that the percentage of bicarbonate decomposition in the boiler depends on the pressure in the boiler. Indeed, it can be assumed that the greater the pressure is in the boiler, the more intense the removal of carbon dioxide with steam is and the more complete the decomposition of bicarbonates is.<\/p>\n

In fact, to a much greater extent, the complete decomposition of bicarbonates in the boiler is affected by the coefficient of evaporation of boiler water and the value of the alkalinity (hydrate) for phenolphthalein of boiler water.<\/p>\n

The fact is that the higher the coefficient of evaporation of boiler water, the longer the temperature effect on 1 liter of feed water of the initial ionic composition is. That is, if the water volume of the steam boiler is 10 m3<\/sup>, the steam capacity is 5.0 t\/h and the salt content of the boiler water is 3000 mg\/l, then the ionic composition (equal to 200 mg\/l) entering the boiler with 1 liter of feed water will be subjected to thermal effect for 30 hours!<\/p>\n

That is\u00a0 \"\"<\/p>\n

During this time, bicarbonate can almost completely decompose.<\/p>\n

However, the greatest impact on the completeness of the decomposition of bicarbonate has the concentration of hydrate in the boiler water. The fact is that the more hydrate in the boiler water, the slower the hydrolysis of carbonates in the boiler water is, because the hydrate in this case is the product of the reaction of hydrolysis of carbonates in the boiler water (1).<\/p>\n

Na2CO3 + \u041d2\u041e <->NaOH + Na\u041d\u0421\u041e3 (1)<\/p>\n

That is, at a certain value of the hydrate, the hydrolysis reaction of carbonates practically stops. There is an equilibrium that can be shifted to the right side only by continuing to reduce the bicarbonate concentration by removing carbon dioxide with steam. But in any case, if the hydrate value in the boiler water is more than 20 mg-EQ\/l, the hydrolysis of carbonates practically stops or has a very slow speed.<\/p>\n

In fact, it turns out that the share of decomposition of bicarbonates in the boiler depends on the concentration of hydrate in the boiler water (phenolphthalein alkalinity).<\/p>\n

To put it quite simply, the ratio of the value of phenolphthalein alkalinity to the total alkalinity of boiler water is equal to the share of decomposition of bicarbonates in the boiler.<\/p>\n

For example,<\/p>\n

The alkalinity of feed water of 2.0 mq-EQ\/l,<\/p>\n

Phenolphthalein alkalinity of boiler water – 20 mg-EQ\/l,<\/p>\n

Total alkalinity of boiler water \u2013 23 mg-EQ\/l,<\/p>\n

Then the share of decomposition of bicarbonates in the boiler is 20\/23=0.87.<\/p>\n

That is, the concentration of carbon dioxide in the steam is 2.0*0.87= 1.74 mg-EQ\/l or 1.74*44=76.56 mg\/l.<\/p>\n

To put it simply, if bicarbonates did not decompose in the boiler, then after evaporation their concentration would be 23 mg-EQ\/l. But since bicarbonates decompose, a hydrate is formed in the boiler, the amount of which is equivalent to the amount of distilled carbon dioxide (20 mg-EQ\/l). And if the total alkalinity was equal to the alkalinity for phenolphthalein, this would indicate that the complete decomposition of bicarbonates occurred in the boiler.<\/p>\n

If the phenolphthalein alkalinity of boiler water is 10 mg-EQ\/l and the total alkalinity is 10.7 mg-EQ\/l, then the share of decomposition of bicarbonates in the boiler is 10\/10. 7=0.93. The concentration of carbon dioxide is 2,0*0,93*44=81.84 mg\/l.<\/p>\n

These data are obtained for the same boiler operating at the same pressure, but with different salinity of boiler water.<\/p>\n

If a thermal deaerator is installed in front of the boiler, the amount of carbon dioxide distilled in it will be equal to the amount of phenolphthalein alkalinity of deaerated water. In this case, the amount of distilled carbon dioxide in the deaerator must be subtracted from the obtained value of the concentration of carbon dioxide in the condensate.<\/p>\n

In the vast majority of cases, the deaerator works primarily to remove free carbon dioxide. After removing free carbon dioxide from the water, hydrate and consequently phenolphthalein alkalinity begin to appear in the water.<\/p>\n

In general, we can write two equations for calculating the concentration of carbon dioxide in steam:<\/p>\n

\"\"\u00a0\u00a0 , mg\/l \u00a0\u00a0\u00a0(2)<\/p>\n

or<\/p>\n

\"\"\u00a0\u00a0\u00a0 , mg\/l\u00a0\u00a0\u00a0 (3)<\/p>\n

where,<\/p>\n

Afeed<\/sub>=Amake-up<\/sub>*(1-\u043a),\u00a0\u00a0 the alkalinity of feed water, mq-EQ\/l,<\/p>\n

\u043a \u2013 share of condensate return,<\/p>\n

Amake-up<\/sub> \u2013 the alkalinity of make-up water, mq-EQ\/l,<\/p>\n

\"\"\u2013 The phenolphthalein alkalinity of boiler water, mq-EQ\/l,<\/p>\n

\"\"\u00a0\u2013 The total alkalinity of boiler water, mq-EQ\/l,<\/p>\n

\"\"\u00a0\u2013 Phenolphthalein alkalinity of deaerated water, mq-EQ\/l,<\/p>\n

\u0430b<\/sub> \u2013 the share of decomposition of bicarbonates in the boiler. Depends on the hydrate concentration in the boiler water. (When the electrical conductivity of boiler water is 1500 \u03bcS\/cm – 0.95; With an electrical conductivity of 6000 \u03bcS\/cm – 0.85)<\/p>\n

\u0430d<\/sub> \u2013 the share of decomposition of bicarbonates in the deaerator. (0.0-0.3).<\/p>\n

Equation (2) can be used for operating boilers, equation (3) for projected boiler houses.<\/p>\n

Thus, reducing the concentration of carbon dioxide in steam can be achieved with the reduction in the alkalinity of feed water by increasing the percentage of condensate return and using water treatment technologies that reduce the alkalinity of the source water.<\/p>\n","protected":false},"excerpt":{"rendered":"

Ivan Tikhonov Steam condensate is corrosive due to the presence of carbon dioxide in it. As a rule, the concentration of carbon dioxide in the condensate is required to be less than 20 mg\/l. The concentration of carbon dioxide in the condensate can be easily determined by knowing the concentration of bicarbonate ion in the […]<\/p>\n","protected":false},"author":2,"featured_media":520,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"categories":[2],"tags":[],"aioseo_notices":[],"post_mailing_queue_ids":[],"_links":{"self":[{"href":"https:\/\/tiwater.info\/en\/wp-json\/wp\/v2\/posts\/587"}],"collection":[{"href":"https:\/\/tiwater.info\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/tiwater.info\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/tiwater.info\/en\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/tiwater.info\/en\/wp-json\/wp\/v2\/comments?post=587"}],"version-history":[{"count":3,"href":"https:\/\/tiwater.info\/en\/wp-json\/wp\/v2\/posts\/587\/revisions"}],"predecessor-version":[{"id":602,"href":"https:\/\/tiwater.info\/en\/wp-json\/wp\/v2\/posts\/587\/revisions\/602"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/tiwater.info\/en\/wp-json\/wp\/v2\/media\/520"}],"wp:attachment":[{"href":"https:\/\/tiwater.info\/en\/wp-json\/wp\/v2\/media?parent=587"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/tiwater.info\/en\/wp-json\/wp\/v2\/categories?post=587"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/tiwater.info\/en\/wp-json\/wp\/v2\/tags?post=587"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}