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Independently, Advanced, High efficiency, Economical

Author:admin Published:2010-01-08 Hits: qq weibo

The application of Nature Sea Water (NSW) FGD

in National Environmental-friendly Projects
 
Yan Weifeng, CEPT
 
 

 

 

I. Foreword

 

NSW FGD, which was developed independently by CEPT, has been applied on Houshi power plant successfully for many years. In 2006, NSW FGD was chosen as “National Excellent Technical Patent Project”, and Houshi power plant received the title of “National Environmental-friendly Project”.


NSW FGD technology has complete independently intellectual property rights in our country, and is granted many invention patents.


This technology is used in coal-firing power plant located along the sea, and it is highly reliable. Houshi power plant(6×600MW) not only realizes over 90% SO2 removal efficiency from seven years ago when the first unit was put into production, but also attains the total running of FGD equipment, which is the only case in China(100% running with generator simultaneously).


Compared with adopting the limestone-method, Houshi power plant can save 5 million cubic meter of water and 180 thousand tons of minerals resource every year, and can avoid producing solid wastes and wastewaters for about 600 thousand tons, at the same time, it reduces the consuming of energy and earth resources by a large volume.


Different with traditional technology, NSW FGD does not need the huge quantity of fresh water and mineral resources; there is no harmful discharging during the whole process. It is a practical resource saving and environmental-friendly technology for large and medium sized fossil-fuel power plant. It is an excellent represent of green science.


In 2005, NDRC confirmed that NSW FGD is one of two applicable FGD methods for large and medium sized power plant (No. [2005]757), and China will make effort to promote the technology that using seawater directly (No. [2005]1561).


If all fossil-fuel power plants along the coast (according to the capacity up to the end of 2005) are installed with NSW FGD, over a hundred billion yuan for operating cost will be reduced, and the discharging waste residue and wastewaters will be eliminated by several millions of tons. Furthermore, hundreds millions of tons of fresh water and tens millions of tons of mineral resources will be saved. Meanwhile, the increasingly serious SO2 and acid rain pollution can be restrained more effectively.


II. Self-owned intellectual property right achievement in China


Both the results of the technical expertise carried by State Intellectual Property Office, Feb 2001and the judicial expertise carried by State Science & Tech Law Society, Nov 2004 indicated clearly that Houshi power plant adopted FGD which is the patent technology owned by CEPT.


As the result of self-owned intellectual property rights strategy, Houshi power plant obtained many “first” in the history of developing large-scale effective cleaning energy, both in China and the world:
The first case that large-scale coal-fired units using NSW FGD for whole flue gas cleaning.
The first case using major craft technic and equipment manufacturing technic belonged to Chinese invention patent.
The first time that realized the simultaneously designing, constructing, and operating of both FGD facility and generator.
The first one, and the only one that can make the FGD and generator running at the same time completely.


In May 2006, the project of Houshi NSW FGD was elected as “National Excellent Technical Patent Project”; in June the same year, it received the title of “National Environmental-friendly Project”.


III. The Scale of Power Plant and the Characteristics of FGD


Houshi Power Plant owned by Huayang Electric Ltd. Co., its construction scale reached 6×600MW(now is expanding for third period construction). 2×600MW in period one and 4×600MW in period two, the two periods construction were started on 1996. 1# unit of period one was finished in Aug 1999 and put into production in Feb 2000; period two was completed in Aug 2004.


It used to purchase MgO-FGD from Japan, but it give up that method then and chose NSW seawater FGD developed by CEPT instead.


The plant annually produce 114300 tons of SO2 in whole (under ECR operating condition), 102900 tons be reduced after FGD treating, the final emitting volume is lower than 11400 tons.


Because no bypass is installed, all the generator and FGD equipments must be kept running together. The first unit has already been put into option for seven years.


No fresh water consumed, no mineral resources or chemical materials needed, and no wastewater or residues discharged. Compared with the MgO, NSW saved 1,500,000 m3 fresh water every year for Houshi power plant, and it also prevented it from transporting 30,000 tons of magnesia from long distance, avoided 1,410,000 m3 wastewater discharging(the discharged water under MgO can not met the environmental protection standard). For comparison, under Limestone Method, it will consume 5,000,000 m3 fresh and 180,000 tons ore annually, and will produce about 600,000 tons waste residue and wastewater every year.


Adopting MgO and Limestone Method, the cost of one kilowatt-hour is respectively 1.3 fens RMB and 2 fens RMB. Under NSW FGD which is adopted by Houshi power plant, the cost is only 0.6 fens RMB per kilowatt-hour. In that case, FGD equipment units were designed for MgO specially; CEPT reconstructed the equipment and used those units as substitutes. The cost will be much lower than that provided by CEPT’s special NSW FGD design.


Among the annual profits of Houshi power plant, hundreds of millions yuan RMB comes from the advance technology, for it saves huge quantities of fresh water and ore resources.


Houshi power plant is the largest coal-fired power plant on running, all equipments and facilities are imported from USA and Japan. The plant adopted supercritical direct-current boiler. The single boiler’s successive exert (under MCR operating condition) is 1,895.99T/h; flue gas volume is 1,765,877Nm3/h, pressure on exit of superheater is 25.35Mpa; supercritical condensing steam turbine. The designed coal type is Australia coal, whose sulfur rate is 0.89%, the calibration sulfur rate is 0.4-1.5%, the annual coal consumption of whole plant is 7.56 million tons. At the end of the boiler there is a double-chamber five-electric-field electrostatic precipitator, whose dust removal rate reaches 99.8%. The boiler uses low NOx burner, and SCR desaltpeterization is set in advance in the end of it.


Flue gas operation volume of single NSW FGD equipment is 1,765,877Nm3/h, and flue gas temperature is 128℃; SO2 concentration in FGD entrance is 1,799mg/Nm3, and below 180mg/Nm3 in exit; seawater flow 69,487m3/h; water quality of FGD system: SO42- increment<68.6mg/l, COD increment<2.5mg/l, pH≥6.5, SS concentration increment 0.16mg/l; SO2 removal efficiency>90%.


The NSW FGD major system is composed by seawater delivering system, flue gas system, absorbing system, seawater quality recovering system, and monitoring and adjusting system. The system contains no gas-bypass or supercharging fans, and does not heat the gas after desulfunzation.


(1) Seawater delivering system
Seawater used for desulfunzation is taken from cycling cooling water of steam condenser exit. Seawater is delivered to the top of the absorber by booster pump to wash SO2 out. Then the acid seawater flows out from the bottom of the absorber, to the seawater quality recovering system. The sprinkle volume varies from different tower design, but the system above can be as high as 39,000m3/h.


(2) Flue gas and sulfur dioxide absorbing system
Dust gas goes through the five-electric-field, and goes into sulfur dioxide absorbing system. It is sprinkled by seawater in absorber so that to spell the sulfur dioxide out.


The sulfur dioxide absorber is one of major equipment of FGD, the system contains two absorbers. Seawater goes in from the top of absorber, and flue gas goes from the bottom. The clean gas is ejected into atmosphere after treating by demister.


The sieve-plate-absorber that owners purchased for MgO was kept, diameter 12m, high 38m, two absorbers for one set. The magnesa deliverer is discarded. After calculating, CEPT believed the equipment can meet the minimum requirement of NSW FGD. Although overmeasure SO2 removal efficiency is low, and operation energy consumption is relatively high, under Houshi power plant’s particular circumstances, if the equipments can be kept as substitutes, it shall reduce the owners lost and lower the total cost. 


(3) Seawater quality recovering system (SQR SYS)
The cooling water from steam condenser is mixed with acid water from absorber in aeration basin. A considerable quantity of air is blow into it so that the dissolve dioxide in seawater is saturated, and converts sulfite into sulfate. During this process, CO2 in seawater is expelled, and then pH returns to the normal level. The aeration fan locates beside aeration basin. The qualified seawater overflows out of aeration basin to barrel-drain, finally into the ocean.


A big space was remained in the plant, which is for making magnesia thick liquid in Japanese MgO tech. This space was just arranged to be SQR aeration basin.


Besides, all equipments for magnesia transferring or treating in MgO are discarded.


IV. Power Plant FGD Building Process


19 April 1996, NPC authorized Houshi power plant, which was exclusively invested for 3.2 billion by Mr. Wang Yongqing, president of FPC (American). Total capacity of Houshi is 6 × 600MW.


Before this project, FPC had stocked 13 total major and supplement sets (including FGD equipments), 600MW capacity. All of them were bought from America and Japan. Seven sets were installed at self-provided power plant for Taiwan Sixth Light Chemical Base (Mailiao), the rest six sets were fixed at Houshi power plant Fujian Province.


On 16 to 18 Jul 1996, MP went through Houshi power plant before the installation. It was found that serious problems existed in MgO FGD equipments bought from FKK------- it was hard to meet the environmental protection standard and difficult to transport raw materials.


In FKK’s MgO, waste waters COD﹥15mg/l (state limit: 5mg/l). It needed a great deal of magnesium mineral and fresh water, the annual magnesium mineral consumption of three projects was respectively: 20,763 tons, 32,016 tons, and 95,523 tons; the average annual fresh water consumption as 49,434 tons. However, Fujian province could not provide the plant magnesium mineral, it must be transported from Liaoning by vacuum package (magnesia is dangerous chemicals) -------long distance and long time. High economic pressure and secondary pollution made desulfunzation------- an exceeding important environmental protection issue into a great obstacle to Houshi plant.


Aug 1996, Mr. Peng Sigan of CEPT sent a mail to Mr. Wang Yongqing, suggested him to adopt NSW-FGD instead of MgO, he also presented his opinion “The FGD Choosing Principles for Enterprise” in writing.


Jan 1997, Mr. Wang requested CEPT to do feasibility research of reconstruction of FGD project, he hoped to discard the MgO and install NSW.


Feb 1997 to Feb 1998, CEPT began to develop and design.


10 Feb 1998, EPA, OA, MP, MA united to censor CEPT’s formal feasible design in Beijing ------ “NSW-FGD Technic and Proposal for Large-scale Coal-fired Power Plant”.


17 Jun 1998, EPA authorized the construction of NSW-FGD for Houshi power plant period one project( 2 × 600MW), provided by CEPT.


26 Aug 1999, Unit 1# was completed and put into production.


22 Feb 2000, EPA authorized Houshi plant period 2 project( 4 × 600MW) go on to use CEPT’s NSW-FGD after site inspection of the working NSW-FGD of period one.


Aug 2004, the total six units as well as their FGD equipments were completed and put into production.


V. Successful Practice of the Harmonious Controlling Three Principles


 In the process of developing and implementing appropriate technic for Houshi, CEPT appealed that it must obey the harmonious controlling three principles so that to control the pollution extensively and efficiently. They are: Clean Controlling, Cost Minimizing, and Adjust Measures to Local Conditions. The successful running of FGD project in Houshi plant is a successful practice of advance ideas represented by the three principles.


1. Clean Controlling

To realize their functions, EP equipments have to consume energy and raw materials, meanwhile discharge related substances. These discharges often lead to “secondary pollution” in certain degree.


Clean Controlling principle requires the effective preventing of secondary pollution in FGD, or limiting its impact in the EP standard. Otherwise, pollutant converts from one form to another, even to a more dangerous one. That is to say, control the pollution while making new pollution. That is widely divergent to the aim of setting EP equipments, and can not fulfill the EP laws and regulations.


To reduce and avoid secondary pollution, it is must to widely adopt advance technics which are low energy-consuming, low material-consuming, and low discharging. This is of great important to environmental protection.
The Clean Controlling principle is as well as environmental friendly principle. NSW-FGD was proven to be a typical environmental friendly technic by succeed of Houshi power plant.


2. Cost Minimizing


To minimize the cost not only connected to the owner’s economic pressure and the economic figure of industrial establishments, for more essential thing, the consumption of capital equals to the consumption of energy and material, and lead to pollutant discharging; seeing from macro view, it means that installation of EP establishments is more a loss than gain. Minimizing the cost signifies decreasing the energy and material consumption, and it also means to reduce the total pollutant discharge volume from the very beginning. It is a positive and fundamental EP measure itself. Saving resources and protecting environment are outside and inside to each other, they supplement each other and can not miss either one.


In fact, Cost Minimizing is resources saving. The truth of seven years running of Houshi FGD projects tells the world powerfully: adopting advance technics do not need significant investment and consuming, moreover, it can insure environmental quality; NSW-FGD is a model case of resource-saving technology.


3. Adjust Measures to Local Condition
Adjust measures to local condition is a basic principle widely followed in many countries. In a successful FGD system, the technic proposal should be a product of adjusting the measures to local condition and optimize choosing, meanwhile are restricted by various aspects as technology, economy, society, and the nature. One FGD system should appear in different ways under different conditions.


So far, there are many kinds of absorbent used for FGD equipments around the world, most of them are calcium-group absorbents. Beyond 85% FGD equipments are using limestone (lime) as major desulfunzation absorbent. The basic reason is most areas stock plenty of limestone, it’s cheap to mine. In other places using magnesium, sodium, or double-alkaline absorbent, there are also abundant alkali resources. All of above are typical cases of the adjusting measures to local condition principle.


Although limestone mines are spread all over the world, some places, especially the places along the coast are short of limestone, both Houshi and Xibu power plants locate on this kind of places. They shall come across huge difficulties if still choose calcium-group absorbents because of going against with the principle.


On the other hand, China is a country seriously lack of water, particular in the coast along areas, the fresh water are very limited. However, the seawater is the only nature resource considered to be inexhaustible. All countries own coastline are actively developing and using the ocean resource. China is also acting actively to push the developing. The fully use of ocean resource will bring great benefit for it can reduce consumption and pollution. Seawater absorbent is a exceptional gift to coast along areas.


For the same reason, whether to recycle or discard the outgrowth also should be decided by the principle. In the consideration of outgrowth recycling ways, it is dangerous to do the recycling just for recycling. More over, it should not make a presumptuous guest usurps the host’s role------ the outgrowth recycling can not override the electric generation. Trying to expend a lot more money on recycling than on the generator, or taking great proportion generated electric to run the recycling system, is as well as putting the cart before the horse.


To sum up, Clean Controlling is the most fundamental principle of environment protect including acid rain controlling; Cost Minimizing and Adjust Measures to Local Condition are two necessities to Clean Controlling. The environment can only be protected efficient only if people fulfill the three principles when choosing and collocating FGD technics.


Houshi power plant’s FGD project adopted self-owned, advanced, high efficiency, economical NSW-FGD. It is a great succeed of self-owned intellectual property right strategy, and also a great succeed of the advance controlling concept which is claimed by ourselves.


VI. Conclusion


 In 2005, NDRC confirmed that NSW FGD is one of two applicable FGD methods for large and medium sized power plant (No. [2005]757), and China will make effort to promote the technology that using seawater directly (No. [2005]1561).

If all fossil-fuel power plants along the coast (according to the capacity up to the end of 2005) are installed with NSW FGD, over a hundred billion yuan for operating cost will be reduced, and the discharging waste residue and wastewaters will be eliminated by several millions of tons. Furthermore, hundreds millions of tons of fresh water and tens millions of tons of mineral resources will be saved. Meanwhile, the increasingly serious SO2 and acid rain pollution can be restrained more effectively.

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