Error: Only variable references are allowed in dynamic SOQL/SOSL.

Hi all, Got stuck in Batch classes not able to execute, getting system.queryexception - Only variable references are allowed in dynamic SOQL/SOSL.

global class SearchAndReplace implements Database.Batchable<sobject>{
global String Query;
global List<id>allObjIds ;
global SearchAndReplace(List<id>allObjectIds){
allObjIds=allObjectIds;
}
global Database.QueryLocator Start(Database.BatchableContext BC){
query='SELECT Id,Name FROM Sobject WHERE Id in:'+allObjIds;
return Database.getQueryLocator(query);
}
global void execute (Database.BatchableContext BC,List<Account>scope){
for(Account obj:scope){
obj.Name='Algoworks';
}
update scope;
}
global void finish (Database.BatchableContext BC){
}
}